Resist composition, method of forming resist pattern and polymeric compound

ABSTRACT

A resist composition including a base component (A) which exhibits changed solubility in a developing solution under action of acid and an acid-generator component (B) which generates acid upon exposure, wherein the base component (A) includes a polymeric compound (A1) having a structural unit (a5) represented by general formula (a5-1). In the formula (a5-1), R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; each of R a  and R b  independently represents a hydrocarbon group which may have a substituent, and R a  and R b  may be mutually bonded to form a ring.

TECHNICAL FIELD

The present invention is related to a resist composition and a method of forming a resist pattern, and a polymeric compound suited for the resist composition.

Priority is claimed on Japanese Patent Application No. 2011-006940, filed Jan. 17, 2011, the content of which is incorporated herein by reference.

BACKGROUND ART

In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.

A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.

In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in the field of pattern miniaturization. Typically, these miniaturization techniques involve shortening the wavelength (increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter (energy higher) than these excimer lasers, such as EB (electron beam), extreme ultraviolet radiation (EUV), and X ray.

As shortening the wavelength of the exposure light source progresses, resist materials for use with these types of exposure light sources require improvement in lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources. As a resist material that satisfies these conditions, a chemically amplified resist composition is known,

For example, in the case where the developing solution is an alkali developing solution (alkali developing process), a chemically amplified resist composition which contains, as a base component (base resin), a resin which exhibits increased solubility in an alkali developing solution under action of acid, and an acid generator is typically used. If the resist film formed using the chemically amplified resist composition is selectively exposed during formation of a resist pattern, then within the exposed portions, acid is generated from the acid-generator component, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution. In this manner, the unexposed portions remain to form a positive resist pattern.

The base resin used exhibits increased polarity by the action of acid, thereby exhibiting increased solubility in an alkali developing solution, whereas the solubility in an organic solvent is decreased. Therefore, when such a base resin is applied to a process using a developing solution containing an organic solvent (organic developing solution) (hereafter, this process is referred to as “solvent developing process” or “negative tone-developing process”) instead of an alkali developing process, the solubility of the exposed portions of the resist film in an organic developing solution is decreased. As a result, the unexposed portions are dissolved and removed by the organic developing solution, and a negative pattern in which the exposed portions remain is formed. The negative tone-developing process is proposed, for example, in Patent Document 1.

Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are now used as base resins for chemically amplified resist compositions that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 2).

Here, the term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position.

Furthermore, currently, in addition to the base resin and the acid generator, a nitrogen-containing organic compound such as an alkylamine, an alkylalcoholamine or the like is added to chemically amplified resist compositions (for example, see Patent Documents 3 and 4). The nitrogen-containing organic compound functions as a quencher which traps the acid generated from the acid generator, and contributes to improving various lithography properties such as a pattern shape and the like.

DOCUMENTS OF RELATED ART Patent Documents

-   [Patent Document 1] Japanese Unexamined Patent Application, First     Publication No. 2008-292975 -   [Patent Document 2] Japanese Unexamined Patent Application, First     Publication No. 2003-241385 -   [Patent Document 3] Japanese Unexamined Patent Application, First     Publication No. H5-249662 -   [Patent Document 4] Japanese Unexamined Patent Application, First     Publication No. H5-232706

SUMMARY OF THE INVENTION

As further progress is expected to be made in lithography techniques and the application field for lithography techniques is expected to expand, development of a novel material for use in lithography will be desired. For example, as miniaturization of resist patterns progresses, improvement will be demanded for resist materials with respect to various lithography properties such as exposure latitude (EL), roughness of the line width (line width roughness (LWR)) and the like, as well as resolution. The roughness, which refers to surface roughness of resist patterns, becomes the cause of defects in the shape of the resist pattern. For example, roughness of the line width (LWR) can cause various defects such as non-uniformity of the line width of line and space patterns. Such defects adversely affect the formation of very fine semiconductor elements, and therefore, improvement thereof is important as the resist pattern becomes more miniaturized.

The present invention takes the above circumstances into consideration, with an object of providing a resist composition which exhibits excellent lithography properties and enables formation of a resist pattern having an excellent shape, and a method of forming a resist pattern using the resist composition, and a polymeric compound suited for the resist composition.

For solving the above-mentioned problems, the present invention employs the following aspects.

Specifically, a first aspect of the present invention is a resist composition including a base component (A) which exhibits changed solubility in a developing solution under action of acid and an acid-generator component (B) which generates acid upon exposure, wherein the base component (A) includes a polymeric compound (A1) having a structural unit (a5) represented by general formula (a5-1) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; each of R^(a) and R^(b) independently represents a hydrocarbon group which may have a substituent, and R^(a) and R^(b) may be mutually bonded to form a ring.

A second aspect of the present invention is a method of forming a resist pattern, including: using a resist composition of the first aspect to form a resist film on a substrate; conducting exposure of the resist film; and alkali-developing the resist film to form a resist pattern.

A third aspect of the present invention is a polymeric compound including a structural unit (a5) represented by general formula (a5-1) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; each of R^(a) and R^(b) independently represents a hydrocarbon group which may have a substituent, and R^(a) and R^(b) may be mutually bonded to form a ring.

In the present description and claims, the term “alkyl group” includes linear, branched or cyclic, monovalent saturated hydrocarbon, unless otherwise specified.

The term “alkylene group” includes linear, branched or cyclic divalent saturated hydrocarbon, unless otherwise specified. The same applies for the alkyl group within an alkoxy group.

A “fluorinated alkyl group” or a “fluorinated alkylene group” is a group in which part or all of the hydrogen atoms of an alkyl group or an alkylene group have been substituted with a fluorine atom.

A “lower alkyl group” is an alkyl group of 1 to 5 carbon atoms.

A “halogenated alkyl group” is a group in which part or all of the hydrogen atoms of an alkyl group are substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.

A “hydroxyalkyl group” is a group in which part or all of the hydrogen atoms of an alkyl group are substituted with a hydroxy group.

The term “aliphatic” is a relative concept used in relation to the term “aromatic”, and defines a group or compound that has no aromaticity.

The term “structural unit” refers to a monomer unit that contributes to the formation of a polymeric compound (polymer, copolymer).

The term “exposure” is used as a general concept that includes irradiation with any form of radiation.

According to the present invention, there are provided a resist composition which exhibits excellent lithography properties and enables formation of a resist pattern having an excellent shape, and a method of forming a resist pattern using the resist composition, and a polymeric compound suited for the resist composition.

MODE FOR CARRYING OUT THE INVENTION

<<Resist Composition>>

The resist composition of the present invention includes a base component (A) which exhibits changed solubility in a developing solution under action of acid (hereafter, referred to as “component (A)”) and an acid-generator component (B) which generates acid upon exposure (hereafter, referred to as “component (B)”).

If the resist film formed using the resist composition is selectively exposed, then within the exposed portions, acid is generated from the component (B), and the action of this acid causes a change in the solubility of the component (A) in a developing solution, whereas the solubility of the component (A) at the unexposed portions in a developing solution remains unchanged. Therefore, a difference of the solubility between the exposed portions and the unexposed portions in a developing solution occurs. In this manner, the exposed portions are dissolved and removed by alkali developing of the resist film in the case of a positive resist pattern, whereas unexposed portions are dissolved and removed in the case of a negative resist pattern, and hence, a resist pattern can be formed.

In the present specification, a resist composition which forms a positive resist pattern is called a positive resist composition, and a resist composition which forms a negative resist pattern is called a negative resist composition.

The resist composition of the present invention in the formation of resist pattern may be used for an alkali developing process in which an alkali developing solution is used in developing treatment, or a solvent developing process (this process is also referred to as “negative tone-developing process”) using a developing solution containing an organic solvent (organic developing solution) in developing treatment.

<Component (A)>

The component (A) is a base component which exhibits changed solubility in a developing solution under action of acid.

In the present description and claims, the term “base component” refers to an organic compound capable of forming a film, and an organic compound having a molecular weight of 500 or more is preferably used as the base component. When the organic compound has a molecular weight of 500 or more, the organic compound exhibits a satisfactory film-forming ability, and a resist pattern of nano level can be easily formed.

The “organic compound having a molecular weight of 500 or more” is broadly classified into non-polymers and polymers.

In general, as a non-polymer, any of those which have a molecular weight in the range of 500 to less than 4,000 is used. Hereafter, a “low molecular weight compound” refers to a non-polymer having a molecular weight in the range of 500 to less than 4,000.

As a polymer, any of those which have a molecular weight of 1,000 or more is generally used. In the present description and claims, the term “polymeric compound” or “resin” refers to a polymer having a molecular weight of 1,000 or more.

With respect to a polymeric compound, the “molecular weight” is the weight average molecular weight in terms of the polystyrene equivalent value determined by gel permeation chromatography (GPC).

In the present invention, the component (A) includes a polymeric compound (A1) (hereafter, referred to as “component (A1)”) having a structural unit (a5) represented by general formula (a5-1).

When the resist composition of the present invention is a “negative resist composition for alkali developing process” which forms a negative pattern in an alkali developing process, for example, as the component (A), a base component that is soluble in an alkali developing solution is used, and a cross-linking agent is blended in the negative resist composition.

In the negative resist composition for alkali developing process, when acid is generated from the component (B) upon exposure, the action of the generated acid causes cross-linking between the base component and the cross-linking agent, and the cross-linked portion becomes insoluble in an alkali developing solution. Therefore, in the formation of a resist pattern, by conducting selective exposure of a resist film formed by applying the negative resist composition onto a substrate, the exposed portions become insoluble in an alkali developing solution, whereas the unexposed portions remain soluble in an alkali developing solution, and hence, a resist pattern can be formed by alkali developing.

In the component (A) for a negative resist composition for alkali developing process, a resin that is soluble in an alkali developing solution (hereafter, referred to as “alkali-soluble resin”) is used as the component (A1).

As the cross-linking agent, at least one selected from the group consisting of a melamine-based cross-linking agent, a urea-based cross-linking agent, an alkylene urea-based cross-linking agent, a glycoluril-based cross-linking agent and an epoxy-based cross-linking agent is preferably used. Typically, a glycoluril-based cross-linking agent having a methylol group or alkoxymethyl group, or the melamine-based cross-linking agent is preferable, as it enables formation of a resist pattern with minimal swelling. The amount of the cross-linker added is preferably within a range from 1 to 50 parts by weight, relative to 100 parts by weight of the alkali-soluble resin.

In the case where the resist composition of the present invention is a resist composition which forms a positive pattern in an alkali developing process and a negative pattern in a solvent developing process, it is preferable to use a base component (A1) which exhibits increased polarity by the action of acid as the component (A). By using the base component which exhibits increased polarity by the action of acid, since the polarity of the base component changes prior to and after exposure, an excellent development contrast can be obtained not only in an alkali developing process, but also in a solvent developing process.

More specifically, in the case of applying an alkali developing process, the component (A1) is substantially insoluble in an alkali developing solution prior to exposure, but when acid is generated from the component (B) upon exposure, the action of this acid causes an increase in the polarity of the base component, thereby increasing the solubility of the component (A1) in an alkali developing solution. Therefore, in the formation of a resist pattern, by conducting selective exposure of a resist film formed by applying the resist composition to a substrate, the exposed portions change from an insoluble state to a soluble state in an alkali developing solution, whereas the unexposed portions remain insoluble in an alkali developing solution, and hence, a positive resist pattern can be formed by alkali developing.

On the other hand, in the case of a solvent developing process, the component (A1) exhibits high solubility in an organic developing solution prior to exposure, and when acid is generated from the component (B) upon exposure, the polarity of the component (A1) is increased by the action of the generated acid, thereby decreasing the solubility of the component (A1) in an organic developing solution. Therefore, in the formation of a resist pattern, by conducting selective exposure of a resist film formed by applying the resist composition to a substrate, the exposed portions change from a soluble state to an insoluble state in an organic developing solution, whereas the unexposed portions remain soluble in an organic developing solution. As a result, by conducting development using an organic developing solution, a contrast can be made between the exposed portions and unexposed portions, thereby enabling the formation of a negative resist pattern.

In the present invention, the component (A1) preferably has, in addition to the structural unit (a5), a structural unit (a1) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and containing an acid decomposable group which exhibits increased polarity by the action of acid. That is, the resist composition of the present invention is preferably a chemically amplified resist composition which becomes a positive type in the case of an alkali developing process, and a negative type in the case of a solvent developing process.

Further, the component (A1) preferably includes, in addition to the structural unit (a5) and the structural unit (a1), at least one structural unit selected from the group consisting of a structural unit (a0) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an —SO₂— containing cyclic group and a structural unit (a2) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains a lactone-containing cyclic group.

Furthermore, it is preferable that the component (A1) include a structural unit (a3) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains a polar group-containing aliphatic hydrocarbon group and, as well as the structural unit (a5) and the structural unit (a1), or the structural unit (a5), the structural unit (a1) and at least one structural unit selected from the group consisting of the structural unit (a0) and the structural unit (a2).

Here, in the present description and claims, a “structural unit derived from an acrylate ester” refers to a structural unit that is formed by the cleavage of the ethylenic double bond of an acrylate ester.

An “acrylate ester” refers to a compound in which the terminal hydrogen atom of the carboxy group of acrylic acid (CH₂═CH—COOH) has been substituted with an organic group.

The acrylate ester may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent. Examples of the substituent which substitutes the hydrogen bonded to the carbon atom on the α-position include an alkyl group of 1 to 5 carbon atoms, a halogenated alkyl group of 1 to 5 carbon atoms and a hydroxyalkyl group. The carbon atom on the α-position of an acrylate ester refers to the carbon atom having the carbonyl group bonded thereto, unless specified otherwise.

Hereafter, an acrylate ester which has the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent is frequently referred to as an “α-position substituted acrylate ester”. Further, the acrylate ester and the α-position substituted acrylate ester are included in and frequently referred to as an “(α-position substituted) acrylate ester”.

With respect to the α-position substituted acrylate ester, the alkyl group as the substituent at the α-position is preferably a linear or branched alkyl group. Specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, and a neopentyl group and the like.

Specific examples of the halogenated alkyl group as the substituent at the α-position include groups in which part or all of the hydrogen atoms of the aforementioned “alkyl group as the substituent at the α-position” are substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable.

It is preferable that a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms be bonded to the α-position of the α-position substituted acrylate ester, a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a fluorinated alkyl group of 1 to 5 carbon atoms is more preferable, and in terms of industrial availability, a hydrogen atom or a methyl group is the most desirable.

[Structural Unit (a5)]

The structural unit (a5) is a structural unit represented by the aforementioned general formula (a5-1).

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; each of R^(a) and R^(b) independently represents a hydrocarbon group which may have a substituent, and R^(a) and R^(b) may be mutually bonded to form a ring.

In formula (a5-1), R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms.

The alkyl group for R is preferably a linear or branched alkyl group, and specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, and a neopentyl group.

Examples of the halogenated alkyl group represented by R include a group in which part or all of the hydrogen atoms of the aforementioned alkyl group of 1 to 5 carbon atoms have been substituted with halogen atoms. Specific examples of the alkyl group include the same as the above-mentioned alkyl group for R. Examples of the halogen atom which substitutes the hydrogen of the alkyl group include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable.

As R, a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a fluorinated alkyl group of 1 to 5 carbon atoms is preferable, and a hydrogen atom or a methyl group is particularly desirable in terms of industrial availability.

In formula (a5-1), each of R^(a) and R^(b) independently represents a hydrocarbon group which may have a substituent.

A hydrocarbon group “has a substituent” means that part or all of the hydrogen atoms within the hydrocarbon group are substituted with substituents (groups or atoms other than hydrogen).

The hydrocarbon group for each of R^(a) and R^(b) may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group.

An “aliphatic hydrocarbon group” refers to a hydrocarbon group that has no aromaticity.

The aliphatic hydrocarbon group may be saturated or unsaturated. In general, the aliphatic hydrocarbon group is preferably saturated.

As specific examples of the aliphatic hydrocarbon group, a linear or branched aliphatic hydrocarbon group, and an aliphatic hydrocarbon group containing a ring in the structure thereof can be given.

With respect to R^(a) and R^(b), the linear or branched aliphatic hydrocarbon group preferably has 1 to 10 carbon atoms, more preferably 1 to 8, still more preferably 1 to 5.

The linear or branched aliphatic hydrocarbon group may or may not have a substituent. Examples of the substituent include a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O).

With respect to R^(a) and R^(b), as examples of the hydrocarbon group containing a ring in the structure thereof, an alicyclic hydrocarbon group (a group in which one or more hydrogen atoms have been removed from an aliphatic hydrocarbon ring), a group in which the alicyclic hydrocarbon group is bonded to the terminal of the linear or branched aliphatic hydrocarbon group and a group in which the alicyclic hydrocarbon group is interposed within the linear or branched aliphatic hydrocarbon group, can be given. As examples of the linear or branched aliphatic hydrocarbon group, the same groups as those described above can be given.

The alicyclic hydrocarbon group preferably has 3 to 20 carbon atoms, and more preferably 3 to 12 carbon atoms.

The alicyclic hydrocarbon group may be either a polycyclic group or a monocyclic group. As the aliphatic hydrocarbon group for the monocyclic group, a group in which one or more hydrogen atoms have been removed from a monocycloalkane is preferable. The monocycloalkane preferably has 3 to 6 carbon atoms, and specific examples thereof include cyclopentane and cyclohexane. As the polycyclic group, a group in which one or more hydrogen atoms have been removed from a polycycloalkane is preferable, and the polycyclic group preferably has 7 to 12 carbon atoms. Examples of the polycycloalkane include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane.

The alicyclic hydrocarbon group may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O).

With respect to R^(a) and R^(b), the aromatic hydrocarbon group is a hydrocarbon group having an aromatic ring.

The aromatic hydrocarbon group for R^(a) and R^(b) preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 10. Here, the number of carbon atoms within a substituent(s) is not included in the number of carbon atoms of the aromatic hydrocarbon group.

Specific examples of the aromatic ring within the aromatic hydrocarbon group include an aromatic hydrocarbon ring such as benzene, biphenyl, fluorene, naphthalene, anthracene, phenanthrene, and an aromatic hetero ring in which part of the carbon atoms constituting the aromatic hydrocarbon ring has been substituted with a heteroatom.

As examples of the heteroatom of the aromatic hetero ring, an oxygen atom, a sulfur atom and a nitrogen atom can be given.

Specific examples of aromatic hydrocarbon groups include a group (aryl group) which is the aromatic hydrocarbon ring having one hydrogen atom removed therefrom, and a group (for example, an arylalkyl group such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethyl group or a 2-naphthylethyl group) in which one hydrogen atom of the aromatic hydrocarbon ring has been substituted with an alkylene group. The alkylene group (an alkyl chain within an arylalkyl group) preferably has 1 to 4 carbon atoms, more preferably 1 or 2, and most preferably 1.

The aromatic hydrocarbon group may or may not have a substituent. For example, a hydrogen atom bonded to the aromatic hydrocarbon ring within the aromatic hydrocarbon group may be substituted with a substituent. As the substituent, an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O) or the like can be used.

The alkyl group as the substituent is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

The alkoxy group as the substituent for is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom as the substituent for the aromatic hydrocarbon group include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

An example of the halogenated alkyl group as the substituent includes a group in which part or all of the hydrogen atoms within the aforementioned alkyl group have been substituted with the aforementioned halogen atoms.

In formula (a5-1), R^(a) and R^(b) may be mutually bonded to form a ring.

The ring may be either a monocyclic group containing an N—C(═O) linkage or a polycyclic group containing an N—C(═O) linkage. Further, the ring may be a hetero ring in which part of the carbon atoms constituting the ring has been substituted with a heteroatom. As examples of the heteroatom of the hetero ring, an oxygen atom, a sulfur atom and a nitrogen atom can be given.

Preferable examples of the structural unit (a5) include structural units represented by general formula (a5-1-1) shown below, since excellent lithography properties are readily obtained.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; X represents CH₂, CH₂CH₂, O, S or SO₂; each of R^(c) and R^(d) independently represents a hydrocarbon group which may have a substituent or a hydrogen atom, and R^(c) and R^(d) may be mutually bonded to form a ring; p represents an integer of 0 to 3.

In formula (a5-1-1), R is the same as defined for R in the aforementioned formula (a5-1).

In formula (a5-1-1), X represents CH₂, CH₂CH₂, O, S or SO₂. Of these, CH₂ is particularly desirable.

In formula (a5-1-1), each of R^(c) and R^(d) independently represents a hydrocarbon group which may have a substituent or a hydrogen atom, and R^(c) and R^(d) may be mutually bonded to form a ring.

Here, the expression “may have a substituent” means that part or all of the hydrogen atoms of a hydrocarbon group may be substituted with a substituent group (atoms other than hydrogen atoms, or groups).

The number of the substituent may be 1 or more.

The hydrocarbon group for each of R^(c) and R^(d) may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group.

The aliphatic hydrocarbon group for each of R^(c) and R^(d) may be either a saturated aliphatic hydrocarbon group, or an unsaturated aliphatic hydrocarbon group. Further, such an aliphatic hydrocarbon group may be linear, branched or cyclic.

As the aliphatic hydrocarbon group for R^(c) and R^(d), a linear or branched saturated hydrocarbon group, a linear or branched monovalent unsaturated hydrocarbon group, or a cyclic aliphatic hydrocarbon group (aliphatic cyclic group) is preferable.

The linear saturated hydrocarbon group (alkyl group) preferably has 1 to 20 carbon atoms, more preferably 1 to 15, and most preferably 1 to 10 (here, the number of carbon atoms within a substituent(s) is not included in the number of carbon atoms of the hydrocarbon group). Specific examples include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decanyl group, an undecyl group, a dodecyl group, a tridecyl group, an isotridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, an isohexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a henicosyl group and a docosyl group.

The branched saturated hydrocarbon group (alkyl group) preferably has 3 to 20 carbon atoms, more preferably 3 to 15, and most preferably 3 to 10 (here, the number of carbon atoms within a substituent(s) is not included in the number of carbon atoms of the hydrocarbon group). Specific examples include a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group and a 4-methylpentyl group.

The unsaturated hydrocarbon group preferably has 2 to 10 carbon atoms, more preferably 2 to 5, and most preferably 2 to 4 (here, the number of carbon atoms within a substituent(s) is not included in the number of carbon atoms of the hydrocarbon group). Examples of linear monovalent unsaturated hydrocarbon groups include a vinyl group, a propenyl group, an allyl group (a 2-propenyl group) and a butynyl group. Examples of branched monovalent unsaturated hydrocarbon groups include a 1-methylvinyl group (—C(CH₃)═CH₂), a 1-methylpropenyl group (—C(CH₃)═CH(CH₃)), a 2-methylpropenyl group (—CH═C(CH₃)₂) and a 2-methyl-2-propenyl group (—CH₂—C(CH₃)═CH₂).

The cyclic aliphatic hydrocarbon group (aliphatic cyclic group) may be either a monocyclic group or a polycyclic group. The aliphatic cyclic group preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 12 (here, the number of carbon atoms within a substituent(s) is not included in the number of carbon atoms of the hydrocarbon group).

As the aliphatic cyclic group, a group in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane can be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

Of these, the aliphatic cyclic group is preferably a polycyclic group, more preferably a group in which one or more hydrogen atoms have been removed from a polycycloalkane, and a group in which one or more hydrogen atoms have been removed from adamantane is particularly desirable.

Further, the aliphatic hydrocarbon group for R^(c) and R^(d) may be a group in which the terminal of an alkylene group is bonded to an aliphatic cyclic group. As examples of the aliphatic cyclic group, the same aliphatic cyclic group as defined above can be given.

The aliphatic hydrocarbon group for R^(c) and R^(d) may have a substituent. For example, part of the carbon atoms constituting the aliphatic hydrocarbon group may be substituted with a substituent group containing a heteroatom, or part or all of the hydrogen atoms of the aliphatic hydrocarbon group may be substituted with a substituent group.

Here, as the “heteroatom”, there is no particular limitation as long as it is an atom other than carbon and hydrogen. Examples of heteroatoms include a halogen atom, an oxygen atom, a sulfur atom and a nitrogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, an iodine atom and a bromine atom.

The substituent group containing a heteroatom may consist of a heteroatom, or may be a group containing a group or atom other than a heteroatom.

Specific examples of the substituent for substituting part of the carbon atoms constituting the aliphatic hydrocarbon group include —O—, —C(═O)—O—, —C(═O)—, —O—C(═O)—O—, —C(═O)—NH—, —NH— (the H may be replaced with a substituent such as an alkyl group or an acyl group), —S—, —S(═O)₂— and —S(═O)₂—O—. When the aliphatic hydrocarbon group is cyclic (aliphatic cyclic group), the aliphatic hydrocarbon group may contain any of these substituent groups in the ring structure.

Examples of the substituent group for substituting part or all of the hydrogen atoms of the aliphatic hydrocarbon group include an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O) and a cyano group. The aforementioned alkoxy group is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group. Examples of the aforementioned halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable. An example of the aforementioned halogenated alkyl group includes a group in which part or all of the hydrogen atoms within an alkyl group of 1 to 5 carbon atoms (e.g., a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group) have been substituted with the aforementioned halogen atoms. When the aliphatic hydrocarbon group is cyclic (aliphatic cyclic group), part or all of the hydrogen atoms of the aliphatic cyclic group may further be substituted with a alkyl group of 1 to 5 carbon atoms.

The aromatic hydrocarbon group for R^(c) and R^(d) is a hydrocarbon group having an aromatic ring. The aromatic hydrocarbon ring preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 12. Here, the number of carbon atoms within a substituent(s) is not included in the number of carbon atoms of the aromatic hydrocarbon group.

Specific examples of aromatic hydrocarbon groups include an aryl group which is an aromatic hydrocarbon ring having one hydrogen atom removed therefrom, such as a phenyl group, a biphenyl group, a fluorenyl group, a naphthyl group, an anthryl group or a phenanthryl group; and an alkylaryl group such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethyl group, or a 2-naphthylethyl group. The alkyl chain within the arylalkyl group preferably has 1 to 4 carbon atoms, more preferably 1 or 2, and most preferably 1.

The aromatic hydrocarbon group for R^(c) and R^(d) may have a substituent. For example, part of the carbon atoms constituting the aromatic ring within the aromatic hydrocarbon group may be substituted with a heteroatom, or a hydrogen atom bonded to the aromatic ring within the aromatic hydrocarbon group may be substituted with a substituent.

In the former example, a heteroaryl group in which part of the carbon atoms constituting the ring within the aforementioned aryl group has been substituted with a heteroatom such as an oxygen atom, a sulfur atom or a nitrogen atom, and a heteroarylalkyl group in which part of the carbon atoms constituting the aromatic hydrocarbon ring within the aforementioned arylalkyl group has been substituted with the aforementioned heteroatom can be used.

In the latter example, as the substituent for the aromatic hydrocarbon group, an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O) or the like can be used.

The alkyl group as the substituent for the aromatic hydrocarbon group is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is more preferable.

The alkoxy group as the substituent for the aromatic hydrocarbon group is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom as the substituent for the aromatic hydrocarbon group include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

An example of the halogenated alkyl group as the substituent for the aromatic hydrocarbon group includes a group in which part or all of the hydrogen atoms within the aforementioned alkyl group have been substituted with the aforementioned halogen atoms.

In formula (a5-1-1), R^(c) and R^(d) may be mutually bonded to form a ring. For example, R^(c) and R^(d) each independently represents a linear or branched alkylene group, and the terminal of R^(c) is bonded to the terminal of R^(d) to form a ring. In such a case, a cyclic group is formed by R^(c), the carbon atom having R^(c) bonded thereto, R^(d), and the carbon atom having R^(d) bonded thereto. Such a cyclic group is preferably a 3- to 10-membered ring, and more preferably 4- to 7-membered ring, and most preferably a 4- to 6-membered ring.

Among the above-mentioned examples, as R^(c) and R^(d), in terms of stability and synthesis, preferably, R^(c) and R^(d) are mutually bonded to form a ring

In formula (a5-1-1), p represents an integer of 0 to 3. In terms of stability, p is preferably 0 or 1, and 0 is particularly desirable.

Specific examples of structural unit (a5) are shown below. In the formulas shown below, R^(α) represents a hydrogen atom, a methyl group or a trifluoromethyl group.

As the structural unit (a5) contained in the component (A1), one type of structural unit may be used, or two or more types may be used in combination.

Among the above-mentioned examples, the structural unit (a5) is preferably a structural unit represented by the aforementioned general formula (a5-1-1). Of these, at least one selected from the group consisting of structural units represented by chemical formulas (a5-1-11), (a5-1-12), (a5-1-14), (a5-1-15) and (a5-1-19) is more preferable, and a structural unit represented by chemical formula (a5-1-11) is particularly desirable.

In the component (A1), the amount of the structural unit (a5) based on the combined total of all structural units constituting the component (A1) is preferably 5 to 50 mol %, more preferably 7 to 45 mol %, still more preferably 10 to 40 mol %, and most preferably 20 to 40 mol %.

When the amount of the structural unit (a5) is at least as large as the lower limit of the above-mentioned range, diffusion of acid generated upon exposure can readily be controlled using a resist composition prepared from the component (A1), and lithography properties such as EL, LWR are improved. On the other hand, when the amount of the structural unit (a5) is no more than the upper limit of the above-mentioned range, good balance can readily be achieved with the other structural units.

[Structural Unit (a1)]

The structural unit (a1) represents a structural unit derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and containing an acid decomposable group which exhibits increased polarity by the action of acid.

The term “acid decomposable group” refers to a group in which at least a part of the bond within the structure thereof is cleaved by the action of an acid generated from the component (B) upon exposure.

Examples of acid decomposable groups which exhibit increased polarity by the action of an acid include groups which are decomposed by the action of an acid to form a polar group.

Examples of the polar group include a carboxy group, a hydroxy group, an amino group and a sulfo group (—SO₃H). Among these, a polar group containing —OH in the structure thereof (hereafter, referred to as “OH-containing polar group”) is preferable, a carboxy group or a hydroxy group is more preferable, and a carboxy group is particularly desirable.

More specifically, as an example of an acid decomposable group, a group in which the aforementioned polar group has been protected with an acid dissociable group (such as a group in which the hydrogen atom of the OH-containing polar group has been protected with an acid dissociable group) can be given.

An “acid dissociable group” is a group in which at least the bond between the acid dissociable group and the adjacent carbon atom is cleaved by the action of an acid generated from the component (B) upon exposure. It is necessary that the acid dissociable group that constitutes the acid decomposable group be a group which exhibits a lower polarity than the polar group generated by the dissociation of the acid dissociable group. Thus, when the acid dissociable group is dissociated by the action of acid, a polar group exhibiting a higher polarity than that of the acid dissociable group is generated, thereby increasing the polarity. As a result, the polarity of the entire component (A1) is increased. By the increase in the polarity, the solubility in a developing solution is relatively changed. When the developing solution is an alkali developing solution, the solubility in the alkali developing solution is increased. On the other hand, when the developing solution is a developing solution containing an organic solvent (organic developing solution), the solubility in the organic developing solution decreases.

As the acid dissociable group, there is no particular limitation, and any of the groups that have been proposed as acid dissociable groups for the base resins of chemically amplified resists can be used. Generally, groups that form either a cyclic or chain-like tertiary alkyl ester with the carboxyl group of the (meth)acrylic acid, and acetal-type acid dissociable groups such as alkoxyalkyl groups are widely known.

Here, a tertiary alkyl ester describes a structure in which an ester is formed by substituting the hydrogen atom of a carboxyl group with a chain-like or cyclic tertiary alkyl group, and a tertiary carbon atom within the chain-like or cyclic tertiary alkyl group is bonded to the oxygen atom at the terminal of the carbonyloxy group (—C(═O)—O—). In this tertiary alkyl ester, the action of acid causes cleavage of the bond between the oxygen atom and the tertiary carbon atom, thereby forming a carboxy group.

The chain-like or cyclic alkyl group may have a substituent.

Hereafter, for the sake of simplicity, groups that exhibit acid dissociability as a result of the formation of a tertiary alkyl ester with a carboxyl group are referred to as “tertiary alkyl ester-type acid dissociable groups”.

Examples of tertiary alkyl ester-type acid dissociable groups include aliphatic branched, acid dissociable groups and aliphatic cyclic group-containing acid dissociable groups.

Here, the term “aliphatic branched” refers to a branched structure having no aromaticity. The “aliphatic branched, acid dissociable group” is not limited to be constituted of only carbon atoms and hydrogen atoms (not limited to hydrocarbon groups), but is preferably a hydrocarbon group. Further, the “hydrocarbon group” may be either saturated or unsaturated, but is preferably saturated.

As an example of the aliphatic branched, acid dissociable groups, for example, a group represented by the formula —C(R⁷¹)(R⁷²)(R⁷³) can be given (in the formula, each of R⁷¹ to R⁷³ independently represents a linear alkyl group of 1 to 5 carbon atoms). The group represented by the formula —C(R⁷¹)(R⁷²)(R⁷³) preferably has 4 to 8 carbon atoms, and specific examples include a tert-butyl group, a 2-methyl-2-butyl group, a 2-methyl-2-pentyl group and a 3-methyl-3-pentyl group.

Among these, a tert-butyl group is particularly desirable.

The term “aliphatic cyclic group” refers to a monocyclic group or polycyclic group that has no aromaticity.

The aliphatic cyclic group within the “aliphatic cyclic group-containing acid dissociable groups” may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, an alkoxy group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O).

The basic ring of the aliphatic cyclic group exclusive of substituents is not limited to be constituted from only carbon and hydrogen (not limited to hydrocarbon groups), but is preferably a hydrocarbon group. Further, the hydrocarbon group may be either saturated or unsaturated, but is preferably saturated.

The aliphatic cyclic group may be monocyclic group, or a polycyclic group.

As such aliphatic cyclic groups, groups in which one or more hydrogen atoms have been removed from a monocycloalkane, and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, which may or may not be substituted with an alkyl group of 1 to 5 carbon atoms, a fluorine atom or a fluorinated alkyl group, may be used. Specific examples include an alicyclic hydrocarbon group such as groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane and cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. In these aliphatic cyclic hydrocarbon groups, part of the carbon atoms constituting the ring may be replaced with an ether group (—O—).

Examples of aliphatic cyclic group-containing acid dissociable groups include

(i) a monovalent aliphatic cyclic group in which a substituent (a group or an atom other than hydrogen) is bonded to the carbon atom on the ring skeleton to which an atom adjacent to the acid dissociable group (e.g., “—O—” within “—C(═O)—O— group”) is bonded to form a tertiary carbon atom; and

(ii) a group which has a branched alkylene group containing a tertiary carbon atom, and a monovalent aliphatic cyclic group to which the tertiary carbon atom is bonded.

In the group (i), as the substituent bonded to the carbon atom to which an atom adjacent to the acid dissociable group on the ring skeleton of the aliphatic cyclic group, an alkyl group can be mentioned. Examples of the alkyl group include the same groups as those represented by R¹⁴ in formulas (1-1) to (1-9) described later.

Specific examples of the group (i) include groups represented by general formulas (1-1) to (1-9) shown below.

Specific examples of the group (ii) include groups represented by general formulas (2-1) to (2-6) shown below.

In the formulas above, R¹⁴ represents an alkyl group; and g represents an integer of 0 to 8.

In the formulas above, each of R¹⁵ and R¹⁶ independently represents an alkyl group.

In general formula (1-1) to (1-9), the alkyl group for R¹⁴ may be any of linear, branched or cyclic, and preferably linear or branched.

The linear alkyl group preferably has 1 to 5 carbon atoms, more preferably 1 to 4, and still more preferably 1 or 2. Specific examples include a methyl group, an ethyl group, an n-propyl group, an n-butyl group and an n-pentyl group. Among these, a methyl group, an ethyl group or an n-butyl group is preferable, and a methyl group or an ethyl group is more preferable.

The branched alkyl group preferably has 3 to 10 carbon atoms, and more preferably 3 to 5. Specific examples of such branched alkyl groups include an isopropyl group, an isobutyl group, a tert-butyl group, an isopentyl group and a neopentyl group, and an isopropyl group is particularly desirable.

g is preferably an integer of 0 to 3, more preferably 1 to 3, and still more preferably 1 or 2.

In formulas (2-1) to (2-6), as the alkyl group for R¹⁵ and R¹⁶, the same alkyl groups as those for R¹⁴ can be used.

In formulas (1-1) to (1-9) and (2-1) to (2-6), part of the carbon atoms constituting the ring may be replaced with an ethereal oxygen atom (—O—).

Further, in formulas (1-1) to (1-9) and (2-1) to (2-6), one or more of the hydrogen atoms bonded to the carbon atoms constituting the ring may be substituted with a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, a fluorine atom and a fluorinated alkyl group.

An “acetal-type acid dissociable group” generally substitutes a hydrogen atom at the terminal of OH-containing polar group such as a carboxy group or hydroxyl group, so as to be bonded with an oxygen atom. When acid is generated upon exposure, the generated acid acts to break the bond between the acetal-type acid dissociable group and the oxygen atom to which the acetal-type, acid dissociable group is bonded, thereby forming an OH-containing polar group such as a carboxy group and a hydroxy group.

Examples of acetal-type acid dissociable groups include groups represented by general formula (p1) shown below.

In the formula, R¹′ and R²′ each independently represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms; n represents an integer of 0 to 3; and Y represents an alkyl group of 1 to 5 carbon atoms or an aliphatic cyclic group.

In general formula (p1) above, n is preferably an integer of 0 to 2, more preferably 0 or 1, and most preferably 0.

As the alkyl group for R¹′ and R²′, the same alkyl groups as those described above for the alkyl groups as the substituent which may be bonded to the carbon atom on the α-position of the aforementioned α-position substituted acrylate ester can be used, although a methyl group or ethyl group is preferable, and a methyl group is particularly desirable.

In the present invention, it is preferable that at least one of R¹′ and R²′ be a hydrogen atom. That is, it is preferable that the acid dissociable group (p1) be a group represented by general formula (p1-1) shown below.

In the formula, R¹′, n and Y are the same as defined above.

As the alkyl group for Y, the same alkyl groups as those described above for the alkyl groups for the substituent which may be bonded to the carbon atom on the α-position of the aforementioned α-position substituted acrylate ester can be mentioned.

As the aliphatic cyclic group for Y, any of the aliphatic monocyclic/polycyclic groups which have been proposed for conventional ArF resists and the like can be appropriately selected for use. For example, the same groups described above in connection with the aliphatic cyclic group within the “aliphatic cyclic group-containing acid dissociable groups” can be used.

As the acetal-type, acid dissociable group, groups represented by general formula (p2) shown below can also be used.

In the formula, R¹⁷ and R¹⁸ each independently represents a linear or branched alkyl group or a hydrogen atom; and R¹⁹ represents a linear, branched or cyclic alkyl group; or R¹⁷ and R¹⁹ each independently represents a linear or branched alkylene group, and the terminal of R¹⁷ is bonded to the terminal of R¹⁹ to form a ring.

The alkyl group for R¹⁷ and R¹⁸ preferably has 1 to 15 carbon atoms, and may be either linear or branched. As the alkyl group, an ethyl group or a methyl group is preferable, and a methyl group is most preferable.

It is particularly desirable that either one of R¹⁷ and R¹⁸ be a hydrogen atom, and the other be a methyl group.

R¹⁹ represents a linear, branched or cyclic alkyl group which preferably has 1 to 15 carbon atoms, and may be any of linear, branched or cyclic.

When R¹⁹ represents a linear or branched alkyl group, it is preferably an alkyl group of 1 to 5 carbon atoms, more preferably an ethyl group or methyl group, and most preferably an ethyl group.

When R¹⁹ represents a cycloalkyl group, it preferably has 4 to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10 carbon atoms. As examples of the cycloalkyl group, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, which may or may not be substituted with a fluorine atom or a fluorinated alkyl group, may be used. Examples of such groups include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. Among these, a group in which one or more hydrogen atoms have been removed from adamantane is preferable.

In general formula (p2) above, R¹⁷ and R¹⁹ may each independently represent a linear or branched alkylene group (preferably an alkylene group of 1 to 5 carbon atoms), and the terminal of R¹⁹ may be bonded to the terminal of R¹⁷.

In such a case, a cyclic group is formed by R¹⁷, R¹⁹, the oxygen atom having R¹⁹ bonded thereto, and the carbon atom having the oxygen atom and R¹⁷ bonded thereto. Such a cyclic group is preferably a 4- to 7-membered ring, and more preferably a 4- to 6-membered ring. Specific examples of the cyclic group include tetrahydropyranyl group and tetrahydrofuranyl group.

Specific examples of the structural unit (a1) include a structural unit represented by general formula (a1-0-1) shown below and a structural unit represented by general formula (a1-0-2) shown below.

In the formulas, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; X¹ represents an acid dissociable group; Y² represents a divalent linking group; and X² represents an acid dissociable group.

In general formula (a1-0-1), as each of the alkyl group and the halogenated alkyl group for R, the same alkyl groups and halogenated alkyl groups as those described above for the alkyl groups and the halogenated alkyl groups as the substituent which may be bonded to the carbon atom on the α-position of the aforementioned α-position substituted acrylate ester can be used, although R is preferably a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a fluorinated alkyl group of 1 to 5 carbon atoms, and a hydrogen atom or a methyl group is particularly desirable.

X¹ is not particularly limited as long as it is an acid dissociable group. Examples thereof include the aforementioned tertiary alkyl ester-type acid dissociable groups and acetal-type acid dissociable groups, and tertiary alkyl ester-type acid dissociable groups are preferable.

In general formula (a1-0-2), R is the same as defined above.

X² is the same as defined for X¹ in general formula (a1-0-1).

The divalent linking group for Y² is not particularly limited, and preferable examples thereof include a divalent hydrocarbon group which may have a substituent and a divalent linking group containing a heteroatom.

A hydrocarbon “has a substituent” means that part or all of the hydrogen atoms within the hydrocarbon group are substituted with substituents (groups or atoms other than hydrogen atom).

The hydrocarbon group may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group.

An “aliphatic hydrocarbon group” refers to a hydrocarbon group that has no aromaticity.

The aliphatic hydrocarbon group as the divalent hydrocarbon group for Y² may be saturated or unsaturated. In general, the aliphatic hydrocarbon group is preferably saturated.

As specific examples of the aliphatic hydrocarbon group, a linear or branched aliphatic hydrocarbon group, and an aliphatic hydrocarbon group containing a ring in the structure thereof can be given.

The linear or branched aliphatic hydrocarbon group preferably has 1 to 10 carbon atoms, more preferably 1 to 6, still more preferably 1 to 4, and most preferably 1 or 3.

As the linear aliphatic hydrocarbon group, a linear alkylene group is preferable. Specific examples thereof include a methylene group [—CH₂—], an ethylene group [—(CH₂)₂—], a trimethylene group [—(CH₂)₃—], a tetramethylene group [—(CH₂)₄—] and a pentamethylene group [—(CH₂)₅—].

As the branched aliphatic hydrocarbon group, branched alkylene groups are preferred, and specific examples include various alkylalkylene groups, including alkylmethylene groups such as —CH(CH₃)—, —CH(CH₂CH₃)—, —C(CH₃)₂—, —C(CH₃)(CH₂CH₃)—, —C(CH₃)(CH₂CH₂CH₃)—, and —C(CH₂CH₃)₂—; alkylethylene groups such as —CH(CH₃)CH₂—, —CH(CH₃)CH(CH₃)—, —C(CH₃)₂CH₂—, —CH(CH₂CH₃)CH₂—, and —C(CH₂CH₃)₂—CH₂—; alkyltrimethylene groups such as —CH(CH₃)CH₂CH₂—, and —CH₂CH(CH₃)CH₂—; and alkyltetramethylene groups such as —CH(CH₃)CH₂CH₂CH₂—, and —CH₂CH(CH₃)CH₂CH₂—. As the alkyl group within the alkylalkylene group, a linear alkyl group of 1 to 5 carbon atoms is preferable.

The linear or branched aliphatic hydrocarbon group may or may not have a substituent. Examples of the substituent include a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O).

As examples of the hydrocarbon group containing a ring in the structure thereof, an alicyclic hydrocarbon group (a group in which two hydrogen atoms have been removed from an aliphatic hydrocarbon ring), a group in which the alicyclic hydrocarbon group is bonded to the terminal of the linear or branched aliphatic hydrocarbon group and a group in which the alicyclic hydrocarbon group is interposed within the linear or branched aliphatic hydrocarbon group, can be given. As examples of the linear or branched aliphatic hydrocarbon group, the same groups as those described above can be given.

The alicyclic hydrocarbon group preferably has 3 to 20 carbon atoms, and more preferably 3 to 12 carbon atoms.

The alicyclic hydrocarbon group may be either a monocyclic group or a polycyclic group. As the monocyclic aliphatic hydrocarbon group, a group in which 2 hydrogen atoms have been removed from a monocycloalkane is preferable. The monocycloalkane preferably has 3 to 6 carbon atoms, and specific examples thereof include cyclopentane and cyclohexane. As the polycyclic group, a group in which two hydrogen atoms have been removed from a polycycloalkane is preferable, and the polycyclic group preferably has 7 to 12 carbon atoms. Examples of the polycycloalkane include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane.

The alicyclic hydrocarbon group may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O).

The aromatic hydrocarbon group is a hydrocarbon group having an aromatic ring.

The aromatic hydrocarbon group as the divalent hydrocarbon group for Y² preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, and most preferably 6 or 15. Of these, 6 to 10 carbon atoms are particularly desirable. Here, the number of carbon atoms within a substituent(s) is not included in the number of carbon atoms of the aromatic hydrocarbon group.

Specific examples of the aromatic ring within the aromatic hydrocarbon group include an aromatic hydrocarbon ring such as benzene, biphenyl, fluorene, naphthalene, anthracene, phenanthrene, and an aromatic hetero ring in which part of the carbon atoms constituting the aromatic hydrocarbon ring has been substituted with a heteroatom. As examples of the heteroatom of the aromatic hetero ring, an oxygen atom, a sulfur atom and a nitrogen atom can be given.

Specific examples of aromatic hydrocarbon groups include a group (arylene group) which is the aromatic hydrocarbon ring having two hydrogen atom removed therefrom, and a group (for example, a group in which one hydrogen atom of the aryl group of an arylalkyl group such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethyl group or a 2-naphthylethyl group further has been removed) in which one hydrogen atom of a group (aryl group) which is the aromatic hydrocarbon ring having one hydrogen atom removed therefrom has been substituted with an alkylene group. The alkylene group (an alkyl chain within an arylalkyl group) preferably has 1 to 4 carbon atoms, more preferably 1 or 2, and most preferably 1.

The aromatic hydrocarbon group may or may not have a substituent. For example, a hydrogen atom bonded to the aromatic hydrocarbon ring within the aromatic hydrocarbon group may be substituted with a substituent. As the substituent, an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O) or the like can be used.

The alkyl group as the substituent is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

The alkoxy group as the substituent for is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom as the substituent for the aromatic hydrocarbon group include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

An example of the halogenated alkyl group as the substituent includes a group in which part or all of the hydrogen atoms within the aforementioned alkyl group have been substituted with the aforementioned halogen atoms.

With respect to a “divalent linking group containing a heteroatom”, a heteroatom is an atom other than carbon and hydrogen, and examples thereof include an oxygen atom, a nitrogen atom, a sulfur atom and a halogen atom.

Examples of the divalent linking group containing a heteroatom include —O—, —C(═O)—O—, —C(═O)—, —O—C(═O)—O—, —C(═O)—NH—, —NH— (H may be substituted with a substituent such as an alkyl group or an acyl group), —S—, —S(═O)₂—, —S(═O)₂—O—, —NH—C(═O)—, ═N—, and a group represented by general formula —Y²¹—O—Y²²—, —[Y²¹—C(═O)—O]_(m)—Y²²— or —Y²¹—O—C(═O)—Y²²— [in the formulas, each of Y²¹ and Y²² independently represents a divalent hydrocarbon group which may have a substituent, O represents an oxygen atom, and m′ represents an integer of 0 to 3].

When Y² represents —NH—, H may be substituted with a substituent such as an alkyl group, an acyl group or the like. The substituent (an alkyl group, an acyl group or the like) preferably has 1 to 10 carbon atoms, more preferably 1 to 8, and most preferably 1 to 5.

In the group represented by the formula —Y²¹—O—Y²²—, —[Y²¹—C(═O)—O]_(m′)—Y²²— or —Y²¹—O—C(═O)—Y²²—, each of Y²¹ and Y²² independently represents a divalent hydrocarbon group which may have a substituent. As the divalent hydrocarbon group, the same groups as those described above for the “divalent hydrocarbon group which may have a substituent” for Y² can be mentioned.

As Y²¹, a linear aliphatic hydrocarbon group is preferable, more preferably a linear alkylene group, still more preferably a linear alkylene group of 1 to 5 carbon atoms, and a methylene group or an ethylene group is particularly desirable.

As Y²², a linear or branched aliphatic hydrocarbon group is preferable, and a methylene group, an ethylene group or an alkylmethylene group is more preferable. The alkyl group within the alkylmethylene group is preferably a linear alkyl group of 1 to 5 carbon atoms, more preferably a linear alkyl group of 1 to 3 carbon atoms, and most preferably a methyl group.

In the group represented by the formula —[Y²¹—C(═O)—O]_(m′)—Y²²—, m′ represents an integer of 0 to 3, preferably an integer of 0 to 2, more preferably 0 or 1, and most preferably 1. Namely, it is particularly desirable that the group represented by the formula —[Y²¹—C(═O)—O]_(m′)—Y²²— is a group represented by the formula —Y²¹—C(═O)—O—Y²²—. Among these, a group represented by the formula —(CH₂)_(a′)—C(═O)—O—(CH₂)_(b′)— is preferable. In the formula, a′ is an integer of 1 to 10, preferably an integer of 1 to 8, more preferably an integer of 1 to 5, still more preferably 1 or 2, and most preferably 1. b′ is an integer of 1 to 10, preferably an integer of 1 to 8, more preferably an integer of 1 to 5, still more preferably 1 or 2, and most preferably 1.

As the divalent linking group containing a heteroatom, a linear group containing an oxygen atom as the heteroatom e.g., a group containing an ether bond or an ester bond is preferable, and a group represented by the aforementioned formula —Y²¹—O—Y²²—, —[Y²¹—C(═O)—O]_(m′)—Y²²— or —Y²¹—O—C(═O)—Y²²— is more preferable.

Among the above-mentioned examples, as the divalent linking group for Y², a linear or branched alkylene group, a divalent alicyclic hydrocarbon group or a divalent linking group containing a heteroatom is particularly desirable. Of these, a linear or branched alkylene group or a divalent linking group containing a heteroatom is most preferable.

Specific examples of the structural unit (a1) include structural units represented by general formulas (a1-1) to (a1-4) shown below.

In the formulas, R, R¹′, R²′, n, Y and Y² are the same as defined above; and X′ represents a tertiary alkyl ester-type acid dissociable group.

Examples of the tertiary alkyl ester-type acid dissociable group for X′ include the same tertiary alkyl ester-type acid dissociable groups.

As R¹′, R²′, n and Y are respectively the same as defined for R¹′, R²′, n and Y in general formula (p1) described above in connection with the “acetal-type acid dissociable group”.

As examples of Y², the same groups as those described above for Y² in general formula (a1-0-2) can be given.

Specific examples of structural units represented by general formula (a1-1) to (a1-4) are shown below.

In the formulas shown below, R^(α) represents a hydrogen atom, a methyl group or a trifluoromethyl group.

In the present invention, as the structural unit (a1), it is preferable to include at least one structural unit selected from the group consisting of a structural unit represented by general formula (a1-0-11) shown below, a structural unit represented by general formula (a1-0-12) shown below, a structural unit represented by general formula (a1-0-13) shown below, a structural unit represented by general formula (a1-0-14) shown below, a structural unit represented by general formula (a1-0-15) shown below and a structural unit represented by general formula (a1-0-2) shown below.

It is particularly desirable that the structural unit (a1) include at least one member selected from the group consisting of a structural unit represented by general formula (a1-0-11) shown below, a structural unit represented by general formula (a1-0-12) shown below, a structural unit represented by general formula (a1-0-13) shown below, a structural unit represented by general formula (a1-0-14) shown below and a structural unit represented by general formula (a1-0-15) shown below.

In the formulas, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R²¹ represents an alkyl group; R²² represents a group which forms an aliphatic monocyclic group with the carbon atom to which R²² is bonded; R²³ represents a branched alkyl group; R²⁴ represents a group which forms an aliphatic polycyclic group with the carbon atom to which R²⁴ is bonded; R²⁵ represents a linear alkyl group of 1 to 5 carbon atoms; each of R¹⁵ and R¹⁶ independently represents an alkyl group; Y² represents a divalent linking group; and X² represents an acid dissociable group.

In the formulas, R, Y² and X² are the same as defined above.

In general formula (a1-0-11), as the alkyl group for R²¹, the same alkyl groups as those described above for R¹⁴ in formulas (1-1) to (1-9) can be used, preferably a methyl group, an ethyl group or an isopropyl group.

As the aliphatic monocyclic group formed by R²² and the carbon atoms to which R²² is bonded, the same aliphatic cyclic groups as those described above for the aforementioned tertiary alkyl ester-type acid dissociable group and which are monocyclic can be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane. The monocycloalkane is preferably a 3- to 11-membered ring, more preferably a 3- to 8-membered ring, still more preferably a 4- to 6-membered ring, and most preferably a 5- or 6-membered ring.

The monocycloalkane may or may not have part of the carbon atoms constituting the ring replaced with an ether bond (—O—).

Further, the monocycloalkane may have a substituent such as an alkyl group of 1 to 5 carbon atoms, a fluorine atom or a fluorinated alkyl group of 1 to 5 carbon atoms.

As an example of R²² constituting such an aliphatic cyclic group, an alkylene group which may have an ether bond (—O—) interposed between the carbon atoms can be given.

Specific examples of structural units represented by general formula (a1-0-11) include structural units represented by the aforementioned formulas (a1-1-16) to (a1-1-23), (a1-1-27) and (a1-1-31). Among these, a structural unit represented by general formula (a1-1-02) shown below which includes the structural units represented by the aforementioned formulas (a1-1-16), (a1-1-17), (a1-1-20) to (a1-1-23), (a1-1-27) and (a1-1-31) is preferable. Further, a structural unit represented by general formula (a1-1-02′) shown below is also preferable.

In the formulas, h is preferably 1 or 2.

In the formulas, R and R²¹ are the same as defined above; and h represents an integer of 1 to 3.

In general formula (a1-0-12), as the branched alkyl group for R²³, the same branched alkyl groups as those described above for R¹⁴ in the aforementioned formulas (1-1) to (1-9) can be used, and an isopropyl group is particularly desirable.

As the aliphatic polycyclic group formed by R²⁴ and the carbon atoms to which R²⁴ is bonded, the same aliphatic cyclic groups as those described above for the aforementioned tertiary alkyl ester-type acid dissociable group and which are polycyclic can be used.

Specific examples of structural units represented by general formula (a1-0-12) include structural units represented by the aforementioned formulas (a1-1-26) and (a1-1-28) to (a1-1-30).

As the structural unit (a1-0-12), a structural unit in which the aliphatic polycyclic group formed by R²⁴ and the carbon atom to which R²⁴ is bonded is a 2-adamantyl group is preferable, and a structural unit represented by the aforementioned formula (a1-1-26) is particularly desirable.

In general formula (a1-0-13), R and R²⁴ are the same as defined above.

As the linear alkyl group for R²⁵, the same linear alkyl groups as those described above for R¹⁴ in the aforementioned formulas (1-1) to (1-9) can be mentioned, and a methyl group or an ethyl group is particularly desirable.

Specific examples of structural units represented by general formula (a1-0-13) include structural units represented by the aforementioned formulas (a1-1-1) to (a1-1-2) and (a1-1-7) to (a1-1-15) which were described above as specific examples of the structural unit represented by general formula (a1-1).

As the structural unit (a1-0-13), a structural unit in which the aliphatic polycyclic group formed by R²⁴ and the carbon atom to which R²⁴ is bonded is a 2-adamantyl group is preferable, and a structural unit represented by the aforementioned formula (a1-1-1) or (a1-1-2) is particularly desirable.

In general formula (a1-0-14), each of R and R²² is the same as defined above. Each of R¹⁵ and R¹⁶ is the same as defined for R¹⁵ and R¹⁶ in general formulas (2-1) to (2-6).

Specific examples of structural units represented by general formula (a1-0-14) include structural units represented by the aforementioned formulas (a1-1-33) and (a1-1-34) which were described above as specific examples of the structural unit represented by general formula (a1-1).

In general formula (a1-0-15), R and R²⁴ are the same as defined above. R¹⁵ and R¹⁶ are the same as defined for R¹⁵ and R¹⁶ in general formulas (2-1) to (2-6).

Specific examples of structural units represented by general formula (a1-0-15) include structural units represented by the aforementioned formulas (a1-1-4) to (a1-1-6) and (a1-1-32) which were described above as specific examples of the structural unit represented by general formula (a1-1).

Examples of structural units represented by general formula (a1-0-2) include structural units represented by the aforementioned formulas (a1-3) and (a1-4). The structural unit represented by formula (a1-3) is particularly desirable.

As a structural unit represented by general formula (a1-0-2), those in which Y² is a group represented by the aforementioned formula —Y²¹—O—Y²²— or —Y²¹—C(═O)—O—Y²²— is particularly desirable.

Preferable examples of such structural units include a structural unit represented by general formula (a1-3-01) shown below, a structural unit represented by general formula (a1-3-02) shown below, and a structural unit represented by general formula (a1-3-03) shown below.

In the formulas, R is the same as defined above; R¹³ represents a hydrogen atom or a methyl group; R¹⁴ represents an alkyl group; e represents an integer of 1 to 10; and n′ represents an integer of 0 to 3.

In the formula, R is as defined above; each of Y²′ and Y²″ independently represents a divalent linking group; X′ represents an acid dissociable group; and w represents an integer of 0 to 3.

In general formulas (a1-3-01) and (a1-3-02), R¹³ is preferably a hydrogen atom.

R¹⁴ is the same as defined for R¹⁴ in the aforementioned formulas (1-1) to (1-9).

e is preferably an integer of 1 to 8, more preferably 1 to 5, and most preferably 1 or 2.

n′ is preferably 1 or 2, and most preferably 2.

Specific examples of structural units represented by general formula (a1-3-01) include structural units represented by the aforementioned formulas (a1-3-25) and (a1-3-26).

Specific examples of structural units represented by general formula (a1-3-02) include structural units represented by the aforementioned formulas (a1-3-27) and (a1-3-28).

In general formula (a1-3-03), as the divalent linking group for Y²′ and Y^(2″), the same groups as those described above for Y² in general formula (a1-3) can be used.

As Y²′, a divalent hydrocarbon group which may have a substituent is preferable, a linear aliphatic hydrocarbon group is more preferable, and a linear alkylene group is still more preferable. Among linear alkylene groups, a linear alkylene group of 1 to 5 carbon atoms is preferable, and a methylene group or an ethylene group is particularly desirable.

As Y^(2″), a divalent hydrocarbon group which may have a substituent is preferable, a linear aliphatic hydrocarbon group is more preferable, and a linear alkylene group is still more preferable. Among linear alkylene groups, a linear alkylene group of 1 to 5 carbon atoms is preferable, and a methylene group or an ethylene group is particularly desirable.

As the acid dissociable group for X′, the same groups as those described above can be used. X′ is preferably a tertiary alkyl ester-type acid dissociable group, more preferably the aforementioned group (i) in which a substituent is bonded to the carbon atom, on the ring skeleton of the monovalent aliphatic cyclic group, to which an atom adjacent to the acid dissociable group is bonded to form a tertiary carbon atom. Among the aforementioned groups (i), a group represented by general formula (1-1) above is preferable.

w represents an integer of 0 to 3, preferably an integer of 0 to 2, more preferably 0 or 1, and most preferably 1.

As the structural unit represented by general formula (a1-3-03), a structural unit represented by general formula (a1-3-03-1) or (a1-3-03-2) shown below is preferable, and a structural unit represented by general formula (a1-3-03-1) is particularly desirable.

In the formulas, R and R¹⁴ are the same as defined above; a′ represents an integer of 1 to 10; b′ represents an integer of 1 to 10; and t represents an integer of 0 to 3.

In general formulas (a1-3-03-1) and (a1-3-03-2), a′ is the same as defined above, preferably an integer of 1 to 8, more preferably 1 to 5, and most preferably 1 or 2.

b′ is the same as defined above, preferably an integer of 1 to 8, more preferably 1 to 5, and most preferably 1 or 2.

t is preferably an integer of 1 to 3, and most preferably 1 or 2.

Specific examples of structural units represented by general formula (a1-3-03-1) or (a1-3-03-2) include structural units represented by the aforementioned formulas (a1-3-29) to (a1-3-32).

As the structural unit (a1) contained in the component (A1), 1 type of structural unit may be used, or 2 or more types may be used.

In the component (A1), the amount of the structural unit (a1) based on the combined total of all structural units constituting the component (A1) is preferably 15 to 70 mol %, more preferably 15 to 60 mol %, still more preferably 20 to 55 mol %. When the amount of the structural unit (a1) is at least as large as the lower limit of the above-mentioned range, a pattern can be easily formed using a resist composition prepared from the component (A1) and also various lithography properties such as sensitivity, resolution, LWR and EL are improved. Further, when the amount of the structural unit (a5) is no more than the upper limit of the above-mentioned range, good balance can readily be achieved with the other structural units.

[Structural Unit (a0)]

The structural unit (a0) is a structural unit derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an —SO₂— containing cyclic group.

By virtue of the structural unit (a0) containing a —SO₂— containing cyclic group, a resist composition containing the component (A1) including the structural unit (a0) is capable of improving the adhesion of a resist film to a substrate. Further, the structural unit (a0) contributes to improvement in various lithography properties such as sensitivity, resolution, exposure latitude (EL margin), LWR (line width roughness), LER (line edge roughness) and mask reproducibility.

Here, an “—SO₂— containing cyclic group” refers to a cyclic group having a ring containing —SO₂— within the ring structure thereof, i.e., a cyclic group in which the sulfur atom (S) within —SO₂— forms part of the ring skeleton of the cyclic group.

In the —SO₂— containing cyclic group, the ring containing —SO₂— within the ring skeleton thereof is counted as the first ring. A cyclic group in which the only ring structure is the ring that contains —SO₂— in the ring skeleton thereof is referred to as a monocyclic group, and a group containing other ring structures is described as a polycyclic group regardless of the structure of the other rings.

The —SO₂— containing cyclic group may be either a monocyclic group or a polycyclic group.

As the —SO₂— containing cyclic group, a cyclic group containing —O—SO₂— within the ring skeleton thereof, i.e., a cyclic group containing a sultone ring in which —O—S— within the —O—SO₂— group forms part of the ring skeleton thereof is particularly desirable.

The —SO₂— containing cyclic group preferably has 3 to 30 carbon atoms, more preferably 4 to 20, still more preferably 4 to 15, and most preferably 4 to 12. Herein, the number of carbon atoms refers to the number of carbon atoms constituting the ring skeleton, excluding the number of carbon atoms within a substituent.

The —SO₂— containing cyclic group may be either a —SO₂— containing aliphatic cyclic group or a —SO₂— containing aromatic cyclic group. A —SO₂— containing aliphatic cyclic group is preferable.

Examples of the —SO₂— containing aliphatic cyclic group include aliphatic cyclic groups in which part of the carbon atoms constituting the ring skeleton has been substituted with a —SO₂— group or a —O—SO₂— group and has at least one hydrogen atom removed from the aliphatic hydrocarbon ring. Specific examples include an aliphatic hydrocarbon ring in which a —CH₂— group constituting the ring skeleton thereof has been substituted with a —SO₂— group and has at least one hydrogen atom removed therefrom; and an aliphatic hydrocarbon ring in which a —CH₂—CH₂— group constituting the ring skeleton has been substituted with a —O—SO₂— group and has at least one hydrogen atom removed therefrom.

The alicyclic hydrocarbon group preferably has 3 to 20 carbon atoms, and more preferably 3 to 12 carbon atoms.

The alicyclic hydrocarbon group may be either a monocyclic group or a polycyclic group. As the monocyclic group, a group in which two hydrogen atoms have been removed from a monocycloalkane of 3 to 6 carbon atoms is preferable. Examples of the monocycloalkane include cyclopentane and cyclohexane. As the polycyclic group, a group in which two hydrogen atoms have been removed from a polycycloalkane of 7 to 12 carbon atoms is preferable. Examples of the polycycloalkane include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane.

The —SO₂— containing cyclic group may have a substituent. Examples of the substituent include an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group, an oxygen atom (═O), —COOR″, —OC(═O)R″ (R″ represents a hydrogen atom or an alkyl group), a hydroxyalkyl group and a cyano group.

The alkyl group for the substituent is preferably an alkyl group of 1 to 6 carbon atoms. Further, the alkyl group is preferably a linear alkyl group or a branched alkyl group. Specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group and a hexyl group. Among these, a methyl group or ethyl group is preferable, and a methyl group is particularly desirable.

As the alkoxy group for the substituent, an alkoxy group of 1 to 6 carbon atoms is preferable. Further, the alkoxy group is preferably a linear alkoxy group or a branched alkyl group. Specific examples of the alkoxy group include the aforementioned alkyl groups for the substituent having an oxygen atom (—O—) bonded thereto.

Examples of the halogen atom for the substituent include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Examples of the halogenated alkyl group for the substituent include groups in which part or all of the hydrogen atoms within the aforementioned alkyl groups have been substituted with the aforementioned halogen atoms.

As examples of the halogenated lower alkyl group for the substituent, groups in which part or all of the hydrogen atoms of the aforementioned alkyl groups for the substituent have been substituted with the aforementioned halogen atoms can be given. As the halogenated alkyl group, a fluorinated alkyl group is preferable, and a perfluoroalkyl group is particularly desirable.

In the —COOR″ group and the —OC(═O)R″ group, R″ is preferably a hydrogen atom or a linear, branched or cyclic alkyl group of 1 to 15 carbon atoms.

When R″ represents a linear or branched alkyl group, it is preferably an alkyl group of 1 to 10 carbon atoms, more preferably an alkyl group of 1 to 5 carbon atoms, and most preferably a methyl group or an ethyl group.

When R″ is a cyclic alkyl group (cycloalkyl group), it preferably has 3 to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10 carbon atoms. As examples of the cycloalkyl group, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, which may or may not be substituted with a fluorine atom or a fluorinated alkyl group, may be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane and cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

The hydroxyalkyl group for the substituent preferably has 1 to 6 carbon atoms, and specific examples thereof include the aforementioned alkyl groups for the substituent in which at least one hydrogen atom has been substituted with a hydroxy group.

More specific examples of the —SO₂— containing cyclic group include groups represented by general formulas (3-1) to (3-4) shown below.

In the formulas, A′ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; z represents an integer of 0 to 2; and R⁶ represents an alkyl group, an alkoxy group, a halogenated alkyl group, a hydroxyl group, —COOR″, —OC(═O)R″, a hydroxyalkyl group or a cyano group, wherein R″ represents a hydrogen atom or an alkyl group.

In general formulas (3-1) to (3-4) above, A′ represents an oxygen atom (—O—), a sulfur atom (—S—) or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom.

As the alkylene group of 1 to 5 carbon atoms represented by A′, a linear or branched alkylene group is preferable, and examples thereof include a methylene group, an ethylene group, an n-propylene group and an isopropylene group.

Examples of alkylene groups that contain an oxygen atom or a sulfur atom include the aforementioned alkylene groups in which —O— or —S— is bonded to the terminal of the alkylene group or present between the carbon atoms of the alkylene group. Specific examples of such alkylene groups include —O—CH₂—, —CH₂—O—CH₂—, —S—CH₂—, —CH₂—S—CH₂—.

As A′, an alkylene group of 1 to 5 carbon atoms or —O— is preferable, more preferably an alkylene group of 1 to 5 carbon atoms, and most preferably a methylene group.

z represents an integer of 0 to 2, and is most preferably 0.

When z is 2, the plurality of R⁶ may be the same or different from each other.

As the alkyl group, alkoxy group, halogenated alkyl group, halogenated alkyl group, hydroxyl group, —COOR″, —OC(═O)R″, hydroxyalkyl group and cyano group for R⁶, the same alkyl groups, alkoxy groups, halogenated alkyl groups, halogenated alkyl groups, hydroxyl groups, —COOR″, —OC(═O)R″, hydroxyalkyl groups and cyano groups as those described above as the substituent which the —SO₂— containing cyclic group may have can be used.

Specific examples of the cyclic groups represented by general formulas (3-1) to (3-4) are shown below. In the formulas shown below, “Ac” represents an acetyl group.

As the —SO₂— containing cyclic group, a group represented by the aforementioned general formula (3-1) is preferable, at least one member selected from the group consisting of groups represented by the aforementioned chemical formulas (3-1-1), (3-1-18), (3-3-1) and (3-4-1) is more preferable, and a group represented by chemical formula (3-1-1) is most preferable.

More specific examples of the structural unit (a0) include structural units represented by general formula (a0-0) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R³ represents a —SO₂— containing cyclic group; and R²⁹′ represents a single bond or a divalent linking group.

In formula (a0-0), R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms.

The alkyl group of 1 to 5 carbon atoms for R is preferably a linear or branched alkyl group of 1 to 5 carbon atoms, and specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group and a neopentyl group.

Examples of the halogenated alkyl group represented by R include a group in which part or all of the hydrogen atoms of the aforementioned alkyl group of 1 to 5 carbon atoms have been substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable.

As R, a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a fluorinated alkyl group of 1 to 5 carbon atoms is preferable, and a hydrogen atom or a methyl group is particularly desirable in terms of industrial availability.

In general formula (a0-0), R³ is the same as defined for the aforementioned —SO₂— containing group.

R²⁹′ may be either a single bond or a divalent linking group. In terms of the effects of the present invention, a divalent linking group is preferable.

As the divalent linking group for R²⁹′, the same divalent linking group as those described above as the divalent linking group for Y² of general formula (a1-0-2) of the aforementioned structural unit (a1) can be used.

As the divalent linking group for R²⁹′, an alkylene group, a divalent alicyclic hydrocarbon group or a divalent linking group containing a heteroatom is preferable. Among these, an alkylene group or a divalent linking group containing an ester bond (—C(═O)—O—) is preferable.

As the alkylene group, a linear or branched alkylene group is preferable. Specific examples include the same linear alkylene groups and branched alkylene groups as those described above for the aliphatic hydrocarbon group represented by Y².

As the divalent linking group containing an ester bond, a group represented by general formula: —R²—C(═O)—O— (in the formula, R² represents a divalent linking group) is particularly desirable. That is, the structural unit (a0) is preferably a structural unit represented by general formula (a0-0-1) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R² represents a divalent linking group; and R³ represents a —SO₂— containing cyclic group.

R² is not particularly limited. For example, the same divalent linking groups as those described for R²⁹′ in general formula (a0-0) can be mentioned.

As the divalent linking group for R², an alkylene group, a divalent alicyclic hydrocarbon group or a divalent linking group containing a heteroatom is preferable.

As the linear or branched alkylene group, the divalent alicyclic hydrocarbon group and the divalent linking group containing a heteroatom, the same linear or branched alkylene group, divalent alicyclic hydrocarbon group and divalent linking group containing a heteroatom as those described above as preferable examples of R²⁹′ can be mentioned.

Among these, a linear or branched alkylene group, or a divalent linking group containing an oxygen atom as a heteroatom is more preferable.

As the linear alkylene group, a methylene group or an ethylene group is preferable, and a methylene group is particularly desirable.

As the branched alkylene group, an alkylmethylene group or an alkylethylene group is preferable, and —CH(CH₃)—, —C(CH₃)₂— or —C(CH₃)₂CH₂— is particularly desirable.

As the divalent linking group containing a heteroatom, a divalent linking group containing an ether bond or an ester bond is preferable, and a group represented by the aforementioned formula —Y²¹—O—Y²²—, formula —[Y²¹—C(═O)—O]_(m′)—Y²²— or formula —Y²¹—O—C(═O)—Y²²— is more preferable. Each of Y²¹, Y²², and m′ is the same as defined above.

Among these, a group represented by the formula —Y²¹—O—C(═O)—Y²²— is preferable, and a group represented by the formula: —(CH₂)_(c)—O—C(═O)—(CH₂)_(d)— is particularly desirable. c represents an integer of 1 to 5, preferably an integer of 1 to 3, and more preferably 1 or 2. d represents an integer of 1 to 5, preferably an integer of 1 to 3 and more preferably 1 or 2.

In particular, as the structural unit (a0), a structural unit represented by general formula (a0-0-11) or (a0-0-12) shown below is preferable, and a structural unit represented by general formula (a0-0-12) shown below is more preferable.

In the formulas, R, A′, R⁶, z and R² are the same as defined above.

In general formula (a0-0-11), A′ is preferably a methylene group, an ethylene group, an oxygen atom (—O—) or a sulfur atom (—S—).

As R², a linear or branched alkylene group or a divalent linking group containing an oxygen atom is preferable. As the linear or branched alkylene group and the divalent linking group containing an oxygen atom represented by R², the same linear or branched alkylene groups and the divalent linking groups containing an oxygen atom as those described above can be mentioned.

As the structural unit represented by general formula (a0-0-12), a structural unit represented by general formula (a0-0-12a) or (a0-0-12b) shown below is particularly desirable.

In the formulas, R and A′ are the same as defined above; and each of c and d is the same as defined above; f represents an integer of 1 to 5 (preferably an integer of 1 to 3).

As the structural unit (a0) contained in the component (A1), 1 type of structural unit may be used, or 2 or more types may be used.

Since the shape of the resist pattern formed using a resist composition containing the component (A1) including the structural unit (a0) is excellent and various lithography properties such as EL margin, LWR and mask reproducibility are excellent, in the component (A1), the amount of the structural unit (a0) based on the combined total of all structural units constituting the component (A1) is preferably 1 to 60 mol %, more preferably 5 to 55 mol %, still more preferably 10 to 50 mol %, and most preferably 15 to 45 mol %.

[Structural Unit (a2)]

The structural unit (a2) represents a structural unit derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains a lactone-containing cyclic group.

The term “lactone-containing cyclic group” refers to a cyclic group including one ring containing a —O—C(═O)— structure (lactone ring). The term “lactone ring” refers to a single ring containing a —O—C(═O)— structure, and this ring is counted as the first ring. A lactone-containing cyclic group in which the only ring structure is the lactone ring is referred to as a monocyclic group, and groups containing other ring structures are described as polycyclic groups regardless of the structure of the other rings.

When the component (A1) is used for forming a resist film, the lactone-containing cyclic group of the structural unit (a2) is effective in improving the adhesion between the resist film and the substrate, and increasing the compatibility with the developing solution (particularly, in the case of an alkali developing process) containing water.

As the structural unit (a2), there is no particular limitation, and an arbitrary structural unit may be used.

Specific examples of lactone-containing monocyclic groups include a group in which one hydrogen atom has been removed from a 4- to 6-membered lactone ring, such as a group in which one hydrogen atom has been removed from β-propiolatone, a group in which one hydrogen atom has been removed from γ-butyrolactone, and a group in which one hydrogen atom has been removed from δ-valerolactone. Further, specific examples of lactone-containing polycyclic groups include groups in which one hydrogen atom has been removed from a lactone ring-containing bicycloalkane, tricycloalkane or tetracycloalkane.

More specifically, examples of the structural unit (a2) include structural units represented by general formulas (a2-1) to (a2-5) shown below.

In the formulas, R represents a hydrogen atom, a lower alkyl group or a halogenated lower alkyl group; each R′ independently represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms, an alkoxy group of 1 to 5 carbon atoms or —COOR″, wherein R″ represents a hydrogen atom or an alkyl group; R²⁹ represents a single bond or a divalent linking group; s″ represents an integer of 0 or 1 to 2; A″ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; and m represents an integer of 0 or 1.

In general formulas (a2-1) to (a2-5), R is the same as defined for R in the structural unit (a1).

Examples of the alkyl group of 1 to 5 carbon atoms for R′ include a methyl group, an ethyl group, a propyl group, an n-butyl group and a tert-butyl group.

Examples of the alkoxy group of 1 to 5 carbon atoms for R′ include a methoxy group, an ethoxy group, an n-propoxy group, an iso-propoxy group, an n-butoxy group and a tert-butoxy group

In terms of industrial availability, R′ is preferably a hydrogen atom.

R″ is preferably a hydrogen atom, or linear, branched or cyclic alkyl group of 1 to 15 carbon atoms.

When R″ is a linear or branched alkyl group, it preferably has 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms.

When R″ is a cyclic alkyl group (cycloalkyl group), it preferably has 3 to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10 carbon atoms. As examples of the cycloalkyl group, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, which may or may not be substituted with a fluorine atom or a fluorinated alkyl group, may be used. Examples of such groups include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

A″ is preferably an alkylene group of 1 to 5 carbon atoms or an —O—, and more preferably an alkylene group of 1 to 5 carbon atoms, and a methylene group is particularly desirable.

R²⁹ represents a single bond or a divalent linking group. The divalent linking group is the same divalent linking groups as those described above for Y² in the aforementioned formula (a1-0-2). Among these, an alkylene group, an ester bond (—C(═O)—O—) or a combination of these is preferable. The alkylene group as a divalent linking group for R²⁹ is preferably a linear or branched alkylene group. Specific examples include the same linear alkylene groups and branched alkylene groups as those described above for the aliphatic hydrocarbon group represented by Y².

s″ is preferably an integer of 1 or 2.

Specific examples of structural units represented by general formulas (a2-1) to (a2-5) are shown below.

In the formulas shown below, R^(α) represents a hydrogen atom, a methyl group or a trifluoromethyl group.

As the structural unit (a2) contained in the component (A1), 1 type of structural unit may be used, or 2 or more types may be used.

The structural unit (a2) is preferably at least one selected from the group consisting of structural units represented by the aforementioned general formulas (a2-1) to (a2-5), and more preferably at least one selected from the group consisting of structural units represented by general formulas (a2-1) to (a2-3). Of these, at least one selected from the group consisting of structural units represented by chemical formulas (a2-1-1), (a2-1-2), (a2-2-1), (a2-2-7), (a2-3-1) and (a2-3-5) is particularly desirable.

In the component (A1), the amount of the structural unit (a2) based on the combined total of all structural units constituting the component (A1) is preferably 5 to 60 mol %, more preferably 10 to 50 mol %, and still more preferably 10 to 45 mol %. When the amount of the structural unit (a2) is at least as large as the lower limit of the above-mentioned range, the effect of using the structural unit (a2) can be satisfactorily achieved. On the other hand, when the amount of the structural unit (a2) is no more than the upper limit of the above-mentioned range, a good balance can readily be achieved with the other structural units.

[Structural Unit (a3)]

The structural unit (a3) represents a structural unit derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains a polar group-containing aliphatic hydrocarbon group (provided that the aforementioned structural units are excluded).

When the component (A1) includes the structural unit (a3), the hydrophilicity of the component (A1) is enhanced, thereby contributing to improvement in resolution.

Examples of the polar group include a hydroxyl group, cyano group, carboxyl group, or hydroxyalkyl group in which some of the hydrogen atoms of the alkyl group have been substituted with fluorine atoms, although a hydroxyl group is particularly desirable.

Examples of the aliphatic hydrocarbon group include linear or branched hydrocarbon groups (preferably alkylene groups) of 1 to 10 carbon atoms, and cyclic aliphatic hydrocarbon groups (cyclic groups). The cyclic groups may be a monocyclic group or a polycyclic group. These cyclic groups can be selected appropriately from the multitude of groups that have been proposed for the resins of resist compositions designed for use with ArF excimer lasers. The cyclic groups are preferably the polycyclic group, and more preferably have 7 to 30 carbon atoms.

Of the various possibilities, structural units derived from an acrylate ester that include an aliphatic polycyclic group that contains a hydroxyl group, cyano group, carboxyl group or a hydroxyalkyl group in which part of the hydrogen atoms of the alkyl group have been substituted with fluorine atoms are particularly desirable. Examples of the polycyclic group include groups in which two or more hydrogen atoms have been removed from a bicycloalkane, tricycloalkane, tetracycloalkane or the like. Specific examples include groups in which two or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. Of these polycyclic groups, groups in which two or more hydrogen atoms have been removed from adamantane, norbornane or tetracyclododecane are preferred industrially.

When the aliphatic hydrocarbon group within the polar group-containing aliphatic hydrocarbon group is a linear or branched hydrocarbon group of 1 to 10 carbon atoms, the structural unit (a3) is preferably a structural unit derived from a hydroxyethyl ester of acrylic acid. On the other hand, when the hydrocarbon group is a polycyclic group, structural units represented by formulas (a3-1), (a3-2) and (a3-3) shown below are preferable.

In the formulas, R is the same as defined above; j is an integer of 1 to 3; k is an integer of 1 to 3; t′ is an integer of 1 to 3; l is an integer of 1 to 5; and s is an integer of 1 to 3.

In general formula (a3-1), j is preferably 1 or 2, and more preferably 1. When j is 2, it is preferable that the hydroxyl groups be bonded to the 3rd and 5th positions of the adamantyl group. When j is 1, it is preferable that the hydroxyl group be bonded to the 3rd position of the adamantyl group.

j is preferably 1, and it is particularly desirable that the hydroxyl group be bonded to the 3rd position of the adamantyl group.

In formula (a3-2), k is preferably 1. The cyano group is preferably bonded to the 5th or 6th position of the norbornyl group.

In formula (a3-3), t′ is preferably 1. l is preferably 1. s is preferably 1. Further, it is preferable that a 2-norbornyl group or 3-norbornyl group be bonded to the terminal of the carboxy group of the acrylic acid. The fluorinated alkylalcohol is preferably bonded to the 5th or 6th position of the norbornyl group.

As the structural unit (a3) contained in the component (A1), one type of structural unit may be used, or two or more types may be used in combination.

In the component (A1), the amount of the structural unit (a3) based on the combined total of all structural units constituting the component (A1) is preferably 5 to 50 mol %, more preferably 5 to 40 mol %, and still more preferably 5 to 25 mol %. When the amount of the structural unit (a3) is at least as large as the lower limit of the above-mentioned range, the effect of using the structural unit (a3) can be satisfactorily achieved. On the other hand, when the amount of the structural unit (a3) is no more than the upper limit of the above-mentioned range, a good balance is readily achieved with the other structural units.

[Other Structural Units]

The component (A1) may also have a structural unit other than the above-mentioned structural units (a5), structural units (a1), structural units (a0), structural units (a2) and structural units (a3), as long as the effects of the present invention are not impaired.

As such another structural unit, any structural unit which cannot be classified as one of the above structural units can be used without any particular limitation, and any of the multitude of conventional structural units used within resist resins for ArF excimer lasers or KrF excimer lasers (and particularly for ArF excimer lasers) can be used.

As examples of such another structural unit, a structural unit (a4) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an acid non-dissociable, aliphatic polycyclic group.

(Structural Unit (a4))

The structural unit (a4) represents a structural unit derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an acid non-dissociable, aliphatic polycyclic group.

With respect to the structural unit (a4), examples of this polycyclic group include the same polycyclic groups as those described above in relation to the aforementioned structural unit (a1), and any of the multitude of conventional polycyclic groups used within the resin component of resist compositions for ArF excimer lasers or KrF excimer lasers (and particularly for ArF excimer lasers) can be used.

In consideration of industrial availability and the like, at least one polycyclic group selected from amongst a tricyclodecyl group, adamantyl group, tetracyclododecyl group, isobornyl group, and norbornyl group is particularly desirable. These polycyclic groups may be substituted with a linear or branched alkyl group of 1 to 5 carbon atoms.

Specific examples of the structural unit (a4) include units with structures represented by general formulas (a4-1) to (a4-5) shown below.

In the formulas, R is the same as defined above.

When such a structural unit (a4) is included in the component (A1), the amount of the structural unit (a4) based on the combined total of all the structural units that constitute the component (A1) is preferably within the range from 1 to 30 mol %, and more preferably from 10 to 20 mol %.

In the resist composition of the present invention, the component (A) contains a polymeric compound (A1) having a structural unit (a5).

Preferable examples of the component (A1) include a polymeric compound having structural units (a5) and (a1).

Specific examples of the component (A1) include a polymeric compound consisting of the structural units (a5) and (a1), a polymeric compound consisting of the structural units (a5), (a1) and (a0), a polymeric compound consisting of the structural units (a5), (a1) and (a3), and a polymeric compound consisting of the structural units (a5), (a1), (a2) and (a3).

In the component (A), as the component (A1), one type of structural unit may be used, or two or more types may be used in combination.

When two or more types of component (A1) are used in combination, the combined total amount of the structural unit (a5) in the two or more types of component (A1) based on the combined total of all the structural units that constitute two or more types of component (A1) is preferably 5 to 50 mol %, more preferably 7 to 45 mol %, still more preferably 10 to 40 mol %, and most preferably 20 to 40 mol %.

When the combined total amount of the structural unit (a5) is at least as large as the lower limit of the above-mentioned range, diffusion of acid generated upon exposure can readily be controlled using a resist composition prepared from the component (A1), and lithography properties such as EL, LWR are improved. On the other hand, when the combined total amount of the structural unit (a5) is no more than the upper limit of the above-mentioned range, good balance can readily be achieved with the other structural units.

The weight average molecular weight (Mw) (the polystyrene equivalent value determined by gel permeation chromatography (GPC)) of the component (A1) is not particularly limited, but is preferably 1,000 to 50,000, more preferably 1,500 to 30,000, and most preferably 2,000 to 20,000. When the weight average molecular weight is no more than the upper limit of the above-mentioned range, the resist composition exhibits a satisfactory solubility in a resist solvent. On the other hand, when the weight average molecular weight is at least as large as the lower limit of the above-mentioned range, dry etching resistance and the cross-sectional shape of the resist pattern become satisfactory.

Further, the dispersity (Mw/Mn) of the component (A1) is not particularly limited, but is preferably 1.0 to 5.0, more preferably 1.0 to 3.0, and most preferably 1.0 to 2.5.

The component (A1) can be obtained, for example, by a conventional radical polymerization or the like of the monomers corresponding with each of the structural units, using a radical polymerization initiator such as azobisisobutyronitrile (AIBN).

Furthermore, in the component (A1), by using a chain transfer agent such as HS—CH₂—CH₂—CH₂—C(CF₃)₂—OH, a —C(CF₃)₂—OH group can be introduced at the terminals of the component (A1). Such a copolymer having introduced a hydroxyalkyl group in which some of the hydrogen atoms of the alkyl group are substituted with fluorine atoms is effective in reducing developing defects and LER (line edge roughness: unevenness of the side walls of a line pattern).

As the monomers for deriving the corresponding structural units, commercially available monomers may be used, or the monomers may be synthesized by a conventional method.

In the resist composition of the present invention, the component (A) may be used in combination with a base component which exhibits increased polarity under action of acid other than the component (A1).

The base component other than the component (A1) is not particularly limited, and any of the multitude of conventional base components used within chemically amplified resist compositions such as a polymeric compound having the aforementioned structural unit (a1) as an essential component, and optionally structural units (a2) to (a4) or (a0), a base resin such as novolak resins and Polyhydroxystyrene (PHS)-based resins, and a low molecular weight compound component can be appropriately selected for use.

Examples of the low molecular weight compound component include a low molecular weight compound having a molecular weight of 500 to less than 4,000 and having an acid dissociable group described above in connection with the component (A1) and a hydrophilic group. Specific examples of the low molecular weight compound include compounds containing a plurality of phenol skeletons in which a part of the hydrogen atoms within hydroxyl groups have been substituted with the aforementioned acid dissociable groups.

In the component (A), the amount of the component (A1) based on the total weight of the component (A) is preferably 25% by weight or more, more preferably 50% by weight or more, still more preferably 75% by weight or more, and may be even 100% by weight. When the amount of the component (A1) is 25% by weight or more, a resist pattern which exhibits higher resolution and higher rectangularity can be readily formed.

In the resist composition of the present invention, the amount of the component (A) can be appropriately adjusted depending on the thickness of the resist film to be formed, and the like.

<Component (B)>

In the resist composition of the present invention, as the component (B), there is no particular limitation, and any of the known acid generators used in conventional chemically amplified resist compositions can be used.

Examples of these acid generators are numerous, and include onium salt acid generators such as iodonium salts and sulfonium salts; oxime sulfonate acid generators; diazomethane acid generators such as bisalkyl or bisaryl sulfonyl diazomethanes and poly(bis-sulfonyl)diazomethanes; nitrobenzylsulfonate acid generators; iminosulfonate acid generators; and disulfone acid generators.

As an onium salt acid generator, a compound represented by general formula (b-1) or (b-2) shown below can be used.

In the formulas above, R¹″ to R³″, R⁵″ and R⁶″ each independently represents an aryl group, alkyl group or alkenyl group which may have a substituent, wherein two of R¹″ to R³″ may be bonded to each other to form a ring with the sulfur atom; and R⁴″ represents an alkyl group, a halogenated alkyl group, an aryl group or an alkenyl group which may have a substituent.

In formula (b-1), R¹″ to R³″ each independently represents an aryl group which may have a substituent, an alkyl group which may have a substituent, and an alkenyl group which may have a substituent. Two of R¹″ to R³″ may be bonded to each other to form a ring with the sulfur atom.

Further, since lithography properties and the shape of the resist pattern are improved, among R¹″ to R³″, at least one is preferably an aryl group, two or more groups are more preferably aryl groups, and it is particularly desirable that all of R¹″ to R³″ be aryl groups.

As examples of the aryl group of R¹″ to R³″, an unsubstituted aryl group of 6 to 20 carbon atoms and a substituted aryl group in which part or all of the hydrogen atoms within the unsubstituted aryl group have been substituted with an alkyl group, an alkoxy group, a halogen atom, a hydroxyl group, an oxo group (═O), an aryl group, an alkoxyalkyloxy group, an alkoxycarbonylalkyloxy group, —C(═O)—O—R⁶′, —O—C(═O)—R⁷′, and —O—R⁸′ can be given. Each of R⁶′, R⁷′ and R⁸′ represents a linear or branched saturated hydrocarbon group of 1 to 25 carbon atoms or a cyclic saturated hydrocarbon group of 3 to 20 carbon atoms, or a linear or branched aliphatic unsaturated hydrocarbon group of 2 to 5 carbon atoms.

With respect to R¹″ to R³″, the unsubstituted aryl group is preferably an aryl group having 6 to 10 carbon atoms because it can be synthesized at a low cost. Specific examples thereof include a phenyl group and a naphthyl group.

The alkyl group as the substituent of the substituted aryl group for R¹″ to R³″ is preferably an alkyl group having 1 to 5 carbon atoms, and most preferably a methyl group, an ethyl group, a propyl group, an n-butyl group, or a tert-butyl group.

The alkoxy group for the substituent of the substituted aryl group is preferably an alkoxy group having 1 to 5 carbon atoms, most preferably a methoxy group, an ethoxy group, an n-propoxy group, an iso-propoxy group, an n-butoxy group or a tert-butoxy group.

The halogen atom for the substituent of the substituted aryl group is preferably a fluorine atom.

As examples of the aryl group for the substituent of the substituted aryl group, the same groups as those described above for the aryl group in R¹″ to R³″ can be given, preferably an aryl group of 6 to 20 carbon atoms, more preferably an aryl group of 6 to 10 carbon atoms, and still more preferably a phenyl group and a naphthyl group.

Examples of the alkoxyalkyloxy group of the substituted aryl group include a group represented by general formula —O—C(R⁴⁷)(R⁴⁸)—O—R⁴⁹ (in the formula, each of R⁴⁷ and R⁴⁸ independently represents a hydrogen atom or a linear or branched alkyl group, and R⁴⁹ represents an alkyl group.

The alkyl group for R⁴⁷ and R⁴⁸ preferably has 1 to 5 carbon atoms, and may be either linear or branched. As the alkyl group, an ethyl group or a methyl group is preferable, and a methyl group is most preferable.

It is preferable that at least one of R⁴⁷ and R⁴⁸ represent a hydrogen atom. It is particularly desirable that at least one of R⁴⁷ and R⁴⁸ represent a hydrogen atom, and the other represent a hydrogen atom or a methyl group.

The alkyl group for R⁴⁹ preferably has 1 to 15 carbon atoms, and may be linear, branched or cyclic.

The linear or branched alkyl group for R⁴⁹ preferably has 1 to 5 carbon atoms. Examples thereof include a methyl group, an ethyl group, a propyl group, an n-butyl group and a tert-butyl group.

The cyclic alkyl group for R⁴⁹ preferably has 4 to 15 carbon atoms, more preferably 4 to 12, and most preferably 5 to 10. Specific examples thereof include groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, and which may or may not be substituted with an alkyl group of 1 to 5 carbon atoms, a fluorine atom or a fluorinated alkyl group. Examples of the monocycloalkane include cyclopentane and cyclohexane. Examples of polycycloalkanes include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane. Among these, a group in which one or more hydrogen atoms have been removed from adamantane is preferable.

Examples of the alkoxycarbonylalkyloxy group of the substituted aryl group include a group represented by general formula —O—R⁵⁰—C(═O)—O—R⁵⁶ (in the formula, R⁵⁰ represents a linear or branched alkylene group, and R⁵⁶ represents a tertiary alkyl group.

The linear or branched alkylene group for R⁵⁰ preferably has 1 to 5 carbon atoms. Examples thereof include a methylene group, an ethylene group, a trimethylene group, a tetramethylene group and a 1,1-dimethylethylene group.

As examples of the tertiary alkyl group for R⁵⁶, a 2-methyl-2-adamantyl group, a 2-ethyl-2-adamantyl group, a 1-methyl-1-cyclopentyl group, a 1-ethyl-1-cyclopentyl group, a 1-methyl-1-cyclohexyl group, a 1-ethyl-1-cyclohexyl group, a 1-(1-adamantyl)-1-methylethyl group, a 1-(1-adamantyl)-1-methylpropyl group, a 1-(1-adamantyl)-1-methylbutyl group, a 1-(1-adamantyl)-1-methylpentyl group, a 1-(1-cyclopentyl)-1-methylethyl group, a 1-(1-cyclopentyl)-1-methylpropyl group, a 1-(1-cyclopentyl)-1-methylbutyl group, a 1-(1-cyclopentyl)-1-methylpentyl group, a 1-(1-cyclohexyl)-1-methylethyl group, a 1-(1-cyclohexyl)-1-methylpropyl group, a 1-(1-cyclohexyl)-1-methylbutyl group, a 1-(1-cyclohexyl)-1-methylpentyl group, a tert-butyl group, a tert-pentyl group, and a tert-hexyl group can be given.

Further, examples include a group in which R⁵⁶ of the aforementioned general formula —O—R⁵⁰—C(═O)—O—R⁵⁶ is replaced by R⁵⁶′. R⁵⁶′ represents an aliphatic cyclic group which may contain a hydrogen atom, an alkyl group, a fluorinated alkyl group or a heteroatom.

As examples of the alkyl group for R⁵⁶′, the same alkyl groups as those described above for R⁴⁹ can be given.

As the fluorinated alkyl group for R⁵⁶′, the aforementioned alkyl group for R⁴⁹ in which part or all of the hydrogen atoms have been substituted with fluorine atoms can be used.

As the aliphatic cyclic group which may contain a heteroatom for R⁵⁶′, an aliphatic cyclic group having no heteroatom, an aliphatic cyclic group containing a heteroatom in the ring structure, an aliphatic cyclic group in which a hydrogen atom thereof has been substituted with a heteroatom can be given.

Examples of the aliphatic cyclic group having no heteroatom for R⁵⁶′ include groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, a tricycloalkane or a tetracycloalkane. Examples of the monocycloalkane include cyclopentane and cyclohexane. Examples of polycycloalkanes include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane. Among these, a group in which one or more hydrogen atoms have been removed from adamantane is preferable.

Specific examples of the aliphatic cyclic group containing a heteroatom in the ring structure for R⁵⁶′ include a group represented by below-described formulas (L1) to (L6) or (S1) to (S4).

Specific examples of the aliphatic cyclic group in which a hydrogen atom thereof has been substituted with a heteroatom for R⁵⁶′ include an aliphatic cyclic group in which a hydrogen atom thereof has been substituted with an oxygen atom (═O).

In formula —C(═O)—O—R⁶′, —O—C(═O)—R⁷′ or —O—R⁸′, each of R⁶′, R⁷′ and R⁸′ represents a linear or branched saturated hydrocarbon group of 1 to 25 carbon atoms or a cyclic saturated hydrocarbon group of 3 to 20 carbon atoms, or a linear or branched aliphatic unsaturated hydrocarbon group of 2 to 5 carbon atoms.

The linear or branched saturated hydrocarbon group has 1 to 25 carbon atoms, preferably 1 to 15 carbon atoms, and more preferably 4 to 10 carbon atoms.

As examples of the linear saturated hydrocarbon group, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group and a decyl group can be used.

As examples of the branched saturated hydrocarbon group, the tertiary alkyl group for R⁵⁶, a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group and a 4-methylpentyl group can be given.

The linear or branched saturated hydrocarbon group may have a substituent. Examples of the substituent include an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group, an oxygen atom (═O), a cyano group and a carboxy group.

The alkoxy group as the substituent for the linear or branched saturated hydrocarbon group is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom as the substituent for the linear or branched saturated hydrocarbon group include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

An example of the halogenated alkyl group as the substituent for the linear or branched saturated hydrocarbon group includes a group in which part or all of the hydrogen atoms within the aforementioned linear or branched saturated hydrocarbon group have been substituted with the aforementioned halogen atoms.

The cyclic saturated hydrocarbon group of 3 to 20 carbon atoms for R⁶′, R⁷′ and R⁸′ may be either a monocyclic group or a polycyclic group. As the aliphatic cyclic group, a group in which one hydrogen atom has been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane can be used. Specific examples include groups in which one hydrogen atom has been removed from a monocycloalkane such as cyclopentane, cyclohexane, cycloheptane or cyclooctane; and groups in which one hydrogen atom has been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

The cyclic saturated hydrocarbon group may have a substituent. For example, part of the carbon atoms constituting the ring within the cyclic alkyl group may be substituted with a heteroatom, or a hydrogen atom bonded to the ring within the cyclic alkyl group may be substituted with a substituent.

In the former example, groups in which one or more hydrogen atoms have been removed from a heterocycloalkane in which part of the carbon atoms constituting the ring within the aforementioned monocycloalkane or polycycloalkane has been substituted with a heteroatom such as an oxygen atom, a sulfur atom or a nitrogen atom can be used. Further, the cyclic saturated hydrocarbon group may have an ester bond (—C(═O)—O—) in the ring structure. Specific examples thereof include lactone-containing monocyclic groups such as a group in which one hydrogen atom has been removed from γ-butyrolactone, and lactone-containing polycyclic groups such as groups in which one hydrogen atom has been removed from a lactone ring-containing bicycloalkane, tricycloalkane or tetracycloalkane.

In the latter example, as the substituent, the same as the above-mentioned substituents which the linear or branched alkyl group may have, lower alkyl groups or the like can be used.

Further, R⁶′, R⁷′ and R⁸′ may be a combination of a linear or branched alkyl group and a cyclic alkyl group.

As examples of a combination of the linear or branched alkyl group and the cyclic alkyl group, a group in which a cyclic alkyl group as a substituent is bonded to a linear or branched alkyl group, and a group in which a linear or branched alkyl group as a substituent is bonded to a cyclic alkyl group can be used.

As examples of the linear aliphatic unsaturated hydrocarbon groups for R⁶′, R⁷′, and R⁸′, a vinyl group, a propenyl group (an allyl group) and a butynyl group can be given.

Examples of branched aliphatic unsaturated hydrocarbon groups for R⁶′, R⁷′ and R⁸′ include a 1-methylpropenyl group and a 2-methylpropenyl group.

The linear or branched aliphatic unsaturated hydrocarbon group may have a substituent. As the substituent, the same as the above-mentioned substituents which the linear or branched alkyl group may have can be used.

With respect to R⁷′ and R⁸′, among the above-mentioned examples, a linear or branched saturated hydrocarbon group of 1 to 15 carbon atoms, or a cyclic saturated hydrocarbon group of 3 to 20 carbon atoms is preferable, since lithography properties and the shape of the resist pattern are excellent.

It is preferable that the aryl group for each of R¹″ to R³″ represent a phenyl group or a naphthyl group.

The alkyl group for R¹″ to R³″ includes, for example, a linear, branched or cyclic alkyl group having 1 to 10 carbon atoms. Among these, in terms of achieving excellent resolution, the alkyl group preferably has 1 to 5 carbon atoms. Specific examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an n-pentyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, a nonyl group, and a decyl group, and a methyl group is most preferable because it is excellent in resolution and can be synthesized at a low cost.

The alkenyl group for R¹″ to R³″ preferably has 2 to 10 carbon atoms, more preferably 2 to 5 carbon atoms, and still more preferably 2 to 4. Specific examples thereof include a vinyl group, a propenyl group (an allyl group), a butynyl group, a 1-methylpropenyl group and a 2-methylpropenyl group.

When two of R¹″ to R³″ are bonded to each other to form a ring with the sulfur atom, it is preferable that the two of R¹″ to R³″ form a 3 to 10-membered ring including the sulfur atom, and it is particularly desirable that the two of R¹″ to R³″ form a 5 to 7-membered ring including the sulfur atom.

When two of R¹″ to R³″ are bonded to each other to form a ring with the sulfur atom, the remaining one of R¹″ to R³″ is preferably an aryl group. As examples of the aryl group, the same as the above-mentioned aryl groups for R¹″ to R³″ can be given.

Specific examples of the cation moiety of a compound represented by the aforementioned formula (b-1) include triphenylsulfonium, (3,5-dimethylphenyl)diphenyl sulfonium, (4-(2-adamantoxymethyloxy)-3,5-dimethylphenyl)diphenylsulfonium, (4-(2-adamantoxymethyloxy)phenyl)diphenylsulfonium, (4-(tert-butoxycarbonylmethyloxy)phenyl)diphenylsulfonium, (4-(tert-butoxycarbonylmethyloxy)-3,5-dimethylphenyl)diphenylsulfonium, (4-(2-methyl-2-adamantyloxycarbonylmethyloxy)phenyl)diphenylsulfonium, (4-(2-methyl-2-adamantyloxycarbonylmethyloxy)-3,5-dimethylphenyl) diphenylsulfonium, tri(4-methylphenyl)sulfonium, dimethyl(4-hydroxynaphthyl)sulfonium, monophenyldimethylsulfonium, diphenylmonomethylsulfonium, (4-methylphenyl)diphenylsulfonium, (4-methoxyphenyl)diphenylsulfonium, tri(4-tert-butyl)phenylsulfonium, diphenyl(1-(4-methoxy)naphthyl)sulfonium, di(1-naphthyl)phenylsulfonium, 1-phenyltetrahydrothiophenium, 1-(4-methylphenyl)tetrahydrothiophenium, 1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiophenium, 1-(4-methoxynaphthalene-1-yl)tetrahydrothiophenium, 1-(4-ethoxynaphthalene-1-yl)tetrahydrothiophenium, 1-(4-n-butoxynaphthalene-1-yl)tetrahydrothiophenium, 1-phenyltetrahydrothiopyranium, 1-(4-hydroxyphenyl)tetrahydrothiopyranium, 1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiopyranium and 1-(4-methylphenyl)tetrahydrothiopyranium.

Further, Preferable examples of the cation moiety of a compound represented by the aforementioned formula (b-1) include specific cation moietys shown below.

In the formula, g1 represents a recurring number, and is an integer of 1 to 5.

In the formula, g2 and g3 represent recurring numbers, wherein g2 is an integer of 0 to 20, and g3 is an integer of 0 to 20.

In formula (b-1) above, R⁴″ represents an alkyl group, a halogenated alkyl group, an aryl group or an alkenyl group which may have a substituent.

The alkyl group for R⁴″ may be any of linear, branched or cyclic.

The linear or branched alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 4 carbon atoms.

The cyclic alkyl group preferably has 4 to 15 carbon atoms, more preferably 4 to 10 carbon atoms, and most preferably 6 to 10 carbon atoms.

As an example of the halogenated alkyl group for R⁴″, a group in which part of or all of the hydrogen atoms of the aforementioned linear, branched or cyclic alkyl group have been substituted with halogen atoms can be given. Examples of the aforementioned halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

In the halogenated alkyl group, the percentage of the number of halogen atoms based on the total number of halogen atoms and hydrogen atoms (halogenation ratio (%)) is preferably 10 to 100%, more preferably 50 to 100%, and most preferably 100%. A higher halogenation ratio is preferable because the acid strength increases.

The aryl group for R⁴″ is preferably an aryl group of 6 to 20 carbon atoms.

The alkenyl group for R⁴″ is preferably an alkenyl group of 2 to 10 carbon atoms.

With respect to R⁴″, the expression “may have a substituent” means that part of or all of the hydrogen atoms within the aforementioned alkyl group, halogenated alkyl group, aryl group or alkenyl group may be substituted with substituents (atoms other than hydrogen atoms, or groups).

R⁴″ may have one substituent, or two or more substituents.

Examples of the substituent include a halogen atom, a heteroatom, an alkyl group, and a group represented by the formula R^(X)-Q¹- (in the formula, Q¹ represents a divalent linking group containing an oxygen atom; and R^(X) represents a hydrocarbon group of 3 to 30 carbon atoms which may have a substituent).

Examples of halogen atoms and alkyl groups as substituents for R⁴″ include the same halogen atoms and alkyl groups as those described above with respect to the halogenated alkyl group for R⁴″.

Examples of heteroatoms include an oxygen atom, a nitrogen atom, and a sulfur atom.

In the group represented by formula R^(X)-Q¹-, Q¹ represents a divalent linking group containing an oxygen atom.

Q¹ may contain an atom other than oxygen. Examples of atoms other than oxygen include a carbon atom, a hydrogen atom, a sulfur atom and a nitrogen atom.

Examples of divalent linking groups containing an oxygen atom include non-hydrocarbon, oxygen atom-containing linking groups such as an oxygen atom (an ether bond; —O—), an ester bond (—C(═O)—O—), an amido bond (—C(═O)—NH—), a carbonyl group (—C(═O)—) and a carbonate bond (—O—C(═O)—O—); and combinations of the aforementioned non-hydrocarbon, heteroatom-containing linking groups with an alkylene group.

Specific examples of the combinations of the aforementioned non-hydrocarbon, heteroatom-containing linking groups and an alkylene group include —R⁹¹—O—, —R⁹²—O—C(═O)—, —C(═O)—O—R⁹³—O—C(═O)— (in the formulas, each of R⁹¹ to R⁹³ independently represents an alkylene group).

The alkylene group for R⁹¹ to R⁹³ is preferably a linear or branched alkylene group, and preferably has 1 to 12 carbon atoms, more preferably 1 to 5, and most preferably 1 to 3.

Specific examples of alkylene groups include a methylene group [—CH₂—]; alkylmethylene groups such as —CH(CH₃)—, —CH(CH₂CH₃)—, —C(CH₃)₂—, —C(CH₃)(CH₂CH₃)—, —C(CH₃)(CH₂CH₂CH₃)— and —C(CH₂CH₃)₂—; an ethylene group [—CH₂CH₂—]; alkylethylene groups such as —CH(CH₃)CH₂—, —CH(CH₃)CH(CH₃)—, —C(CH₃)₂CH₂— and —CH(CH₂CH₃)CH₂—; a trimethylene group (n-propylene group) [—CH₂CH₂CH₂—]; alkyltrimethylene groups such as —CH(CH₃)CH₂CH₂— and —CH₂CH(CH₃)CH₂—; a tetramethylene group [—CH₂CH₂CH₂CH₂—]; alkyltetramethylene groups such as —CH(CH₃)CH₂CH₂CH₂— and —CH₂CH(CH₃)CH₂CH₂—; and a pentamethylene group [—CH₂CH₂CH₂CH₂CH₂—].

Q¹ is preferably a divalent linking group containing an ester linkage or ether linkage, and more preferably a group of —R⁹¹—O—, —R⁹²—O—C(═O)— or —C(═O)—O—R⁹³—O—C(═O)—.

In the group represented by the formula R^(X)-Q¹-, the hydrocarbon group for R^(X) may be either an aromatic hydrocarbon group or an aliphatic hydrocarbon group.

The aromatic hydrocarbon group is a hydrocarbon group having an aromatic ring. The aromatic hydrocarbon ring preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 12. Here, the number of carbon atoms within a substituent(s) is not included in the number of carbon atoms of the aromatic hydrocarbon group.

Specific examples of aromatic hydrocarbon groups include an aryl group which is an aromatic hydrocarbon ring having one hydrogen atom removed therefrom, such as a phenyl group, a biphenyl group, a fluorenyl group, a naphthyl group, an anthryl group or a phenanthryl group; and an alkylaryl group such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethyl group, or a 2-naphthylethyl group. The alkyl chain within the arylalkyl group preferably has 1 to 4 carbon atoms, more preferably 1 or 2, and most preferably 1.

The aromatic hydrocarbon group may have a substituent. For example, part of the carbon atoms constituting the aromatic ring within the aromatic hydrocarbon group may be substituted with a heteroatom, or a hydrogen atom bonded to the aromatic ring within the aromatic hydrocarbon group may be substituted with a substituent.

In the former example, a heteroaryl group in which part of the carbon atoms constituting the ring within the aforementioned aryl group has been substituted with a heteroatom such as an oxygen atom, a sulfur atom or a nitrogen atom, and a heteroarylalkyl group in which part of the carbon atoms constituting the aromatic hydrocarbon ring within the aforementioned arylalkyl group has been substituted with the aforementioned heteroatom can be used.

In the latter example, as the substituent for the aromatic hydrocarbon group, an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O) or the like can be used.

The alkyl group as the substituent for the aromatic hydrocarbon group is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

The alkoxy group as the substituent for the aromatic hydrocarbon group is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom as the substituent for the aromatic hydrocarbon group include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

An example of the halogenated alkyl group as the substituent for the aromatic hydrocarbon group includes a group in which part or all of the hydrogen atoms within the aforementioned alkyl group have been substituted with the aforementioned halogen atoms.

The aliphatic hydrocarbon group for R^(X) may be either a saturated aliphatic hydrocarbon group, or an unsaturated aliphatic hydrocarbon group. Further, the aliphatic hydrocarbon group may be linear, branched or cyclic.

In the aliphatic hydrocarbon group for R^(X), part of the carbon atoms constituting the aliphatic hydrocarbon group may be substituted with a substituent group containing a heteroatom, or part or all of the hydrogen atoms constituting the aliphatic hydrocarbon group may be substituted with a substituent group containing a heteroatom.

As the “heteroatom” for R^(X), there is no particular limitation as long as it is an atom other than carbon and hydrogen. Examples of heteroatoms include a halogen atom, an oxygen atom, a sulfur atom and a nitrogen atom.

Examples of the halogen atom include a fluorine atom, a chlorine atom, an iodine atom and a bromine atom.

The substituent group containing a heteroatom may consist of a heteroatom, or may be a group containing a group or atom other than a heteroatom.

Specific examples of the substituent group for substituting part of the carbon atoms include —O—, —C(═O)—O—, —C(═O)—, —O—C(═O)—O—, —C(═O)—NH—, —NH— (the H may be replaced with a substituent such as an alkyl group or an acyl group), —S—, —S(═O)₂— and —S(═O)₂—O—. When the aliphatic hydrocarbon group is cyclic, the aliphatic hydrocarbon group may contain any of these substituent groups in the ring structure.

Examples of the substituent group for substituting part or all of the hydrogen atoms include an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O) and a cyano group.

The aforementioned alkoxy group is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the aforementioned halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

An example of the aforementioned halogenated alkyl group includes a group in which part or all of the hydrogen atoms within an alkyl group of 1 to 5 carbon atoms (e.g., a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group) have been substituted with the aforementioned halogen atoms.

As the aliphatic hydrocarbon group, a linear or branched saturated hydrocarbon group, a linear or branched monovalent unsaturated hydrocarbon group, or a cyclic aliphatic hydrocarbon group (aliphatic cyclic group) is preferable.

The linear saturated hydrocarbon group (alkyl group) preferably has 1 to 20 carbon atoms, more preferably 1 to 15, and most preferably 1 to 10. Specific examples include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decanyl group, an undecyl group, a dodecyl group, a tridecyl group, an isotridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, an isohexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a henicosyl group and a docosyl group.

The branched saturated hydrocarbon group (alkyl group) preferably has 3 to 20 carbon atoms, more preferably 3 to 15, and most preferably 3 to 10. Specific examples include a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group and a 4-methylpentyl group.

The unsaturated hydrocarbon group preferably has 2 to 10 carbon atoms, more preferably 2 to 5, still more preferably 2 to 4, and most preferably 3. Examples of linear monovalent unsaturated hydrocarbon groups include a vinyl group, a propenyl group (an allyl group) and a butynyl group. Examples of branched monovalent unsaturated hydrocarbon groups include a 1-methylpropenyl group and a 2-methylpropenyl group.

Among the above-mentioned examples, as the unsaturated hydrocarbon group, a propenyl group is particularly desirable.

The aliphatic cyclic group may be either a monocyclic group or a polycyclic group. The aliphatic cyclic group preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 12.

As the aliphatic cyclic group, a group in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane can be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

When the aliphatic cyclic group does not contain a heteroatom-containing substituent group in the ring structure thereof, the aliphatic cyclic group is preferably a polycyclic group, more preferably a group in which one or more hydrogen atoms have been removed from a polycycloalkane, and a group in which one or more hydrogen atoms have been removed from adamantane is particularly desirable.

When the aliphatic cyclic group contains a heteroatom-containing substituent group in the ring structure thereof, the heteroatom-containing substituent group is preferably —O—, —C(═O)—O—, —S—, —S(═O)₂— or —S(═O)₂—O—. Specific examples of such aliphatic cyclic groups include groups represented by formulas (L1) to (L6) and (S1) to (S4) shown below.

In the formula, Q″ represents an alkylene group of 1 to 5 carbon atoms, —O—, —S—, —O—R⁹⁴— or —S—R⁹⁵— (wherein each of R⁹⁴ and R⁹⁵ independently represents an alkylene group of 1 to 5 carbon atoms); and m represents 0 or 1.

As the alkylene group for Q″, R⁹⁴ and R⁹⁵, the same alkylene groups as those described above for R⁹¹ to R⁹³ can be used.

In these aliphatic cyclic groups, part of the hydrogen atoms bonded to the carbon atoms constituting the ring structure may be substituted with a substituent. Examples of substituents include an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group and an oxygen atom (═O).

As the alkyl group, an alkyl group of 1 to 5 carbon atoms is preferable, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

As the alkoxy group and the halogen atom, the same groups as the substituent groups for substituting part or all of the hydrogen atoms can be used.

Among the above-mentioned examples, as such R^(X), a cyclic group which may have a substituent is preferable. The cyclic group may be either an aromatic hydrocarbon group which may have a substituent, or an aliphatic cyclic group which may have a substituent, and an aliphatic cyclic group which may have a substituent is preferable.

As the aromatic hydrocarbon group, a naphthyl group which may have a substituent, or a phenyl group which may have a substituent is preferable.

As the aliphatic cyclic group which may have a substituent, an aliphatic polycyclic group which may have a substituent is preferable. As the aliphatic polycyclic group, the aforementioned group in which one or more hydrogen atoms have been removed from a polycycloalkane, and groups represented by the aforementioned formulas (L2) to (L5), (S3) and (S4) are preferable.

Further, it is particularly desirable that R^(X) have a polar moiety, because it results in improved lithographic properties and resist pattern shape.

Specific examples of R^(X) having a polar moiety include those in which a part of the carbon atoms constituting the aliphatic hydrocarbon group for X is substituted with a substituent group containing a heteroatom such as —O—, —C(═O)—O—, —C(═O)—, —O—C(═O)—O—, —C(═O)—NH—, —NH— (wherein H may be substituted with a substituent such as an alkyl group or an acyl group), —S—, —S(═O)₂— and —S(═O)₂—O—.

Among the above-mentioned examples, R⁴″ preferably has R^(X)-Q¹- as a substituent. In such a case, R⁴″ is preferably a group represented by the formula R^(X)-Q¹-Y¹— (in the formula, Q¹ and R^(X) are the same as defined above; and Y¹ represents an alkylene group of 1 to 4 carbon atoms which may have a substituent, or a fluorinated alkylene group of 1 to 4 carbon atoms which may have a substituent).

In the group represented by the formula R^(X)-Q¹-Y¹—, as the alkylene group for Y¹, the same alkylene group as those described above for Q¹ in which the number of carbon atoms is 1 to 4 can be used.

As the fluorinated alkylene group for Y¹, the aforementioned alkylene group in which part or all of the hydrogen atoms have been substituted with fluorine atoms can be used.

Specific examples of Y¹ include —CF₂CF₂—, —CF₂CF₂CF₂—, —CF(CF₃)CF₂—, —CF(CF₂CF₃)—, —C(CF₃)₂—, —CF₂CF₂CF₂CF₂—, —CF(CF₃)CF₂CF₂—, —CF₂CF(CF₃)CF₂—, —CF(CF₃)CF(CF₃)—, —C(CF₃)₂CF₂—, —CF(CF₂CF₃)CF₂—, —CF(CF₂CF₂CF₃)—, —C(CF₃)(CF₂CF₃)—; —CHF—, —CH₂CF₂—, —CH₂CH₂CF₂—, —CH₂CF₂CF₂—, —CH(CF₃)CH₂—, —CH(CF₂CF₃)—, —C(CH₃)(CF₃)—, —CH₂CH₂CH₂CF₂—, —CH₂CH₂CF₂CF₂—, —CH(CF₃)CH₂CH₂—, —CH₂CH(CF₃)CH₂—, —CH(CF₃)CH(CF₃)—, —C(CF₃)₂CH₂—; —CH₂CH₂—, —CH₂CH₂CH₂—, —CH(CH₃)CH₂—, —CH(CH₂CH₃)—, —C(CH₃)₂—, —CH₂CH₂CH₂CH₂—, —CH(CH₃)CH₂CH₂—, —CH₂CH(CH₃)CH₂—, —CH(CH₃)CH(CH₃)—, —C(CH₃)₂CH₂—, —CH(CH₂CH₃)CH₂—, —CH(CH₂CH₂CH₃)—, and —C(CH₃)(CH₂CH₃)—.

Y¹ is preferably a fluorinated alkylene group, and particularly preferably a fluorinated alkylene group in which the carbon atom bonded to the adjacent sulfur atom is fluorinated. Examples of such fluorinated alkylene groups include —CF₂CF₂—, —CF₂CF₂CF₂—, —CF(CF₃)CF₂—, —CF₂CF₂CF₂CF₂—, —CF(CF₃)CF₂CF₂—, —CF₂CF(CF₃)CF₂—, —CF(CF₃)CF(CF₃)—, —C(CF₃)₂CF₂—, —CF(CF₂CF₃)CF₂—; —CH₂CF₂—, —CH₂CH₂CF₂—, —CH₂CF₂CF₂—; —CH₂CH₂CH₂CF₂—, —CH₂CH₂CF₂CF₂—, and —CH₂CF₂CF₂CF₂—.

Of these, —CF₂CF₂—, —CF₂CF₂CF₂— or CH₂CF₂CF₂— is preferable, —CF₂CF₂— or —CF₂CF₂CF₂— is more preferable, and —CF₂— is particularly desirable.

The alkylene group or fluorinated alkylene group may have a substituent. The alkylene group or fluorinated alkylene group “has a substituent” means that part or all of the hydrogen atoms or fluorine atoms in the alkylene group or fluorinated alkylene group have been substituted with groups other than hydrogen atoms and fluorine atoms.

Examples of substituents which the alkylene group or fluorinated alkylene group may have include an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, and a hydroxyl group.

In formula (b-2), each of R⁵″ and R⁶″ independently represents an aryl group, alkyl group or alkenyl group which may have a substituent.

Further, since lithography properties and the shape of the resist pattern are improved, among R⁵″ and R⁶″, at least one is preferably aryl group. It is more preferable that both R⁵″ and R⁶″ represent an aryl group.

As the aryl group for R⁵″ and R⁶″, the same as the aryl groups for R¹″ to R³″ can be used.

As the alkyl group for R⁵″ and R⁶″, the same as the alkyl groups for R¹″ to R³″ can be used.

As the alkenyl group for R⁵″ and R⁶″, the same as the alkenyl groups for R¹″ to R³″ can be used.

It is particularly desirable that both of R⁵″ and R⁶″ represent a phenyl group.

Specific examples of the cation moiety of a compound represented by general formula (b-2) include diphenyliodonium and bis(4-tert-butylphenyl)iodonium.

As R⁴″ in formula (b-2), the same groups as those mentioned above for R⁴″ in formula (b-1) can be used.

Specific examples of suitable onium salt acid generators represented by formula (b-1) or (b-2) include diphenyliodonium trifluoromethanesulfonate or nonafluorobutanesulfonate; bis(4-tert-butylphenyl)iodonium trifluoromethanesulfonate or nonafluorobutanesulfonate; triphenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; tri(4-methylphenyl)sulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; dimethyl(4-hydroxynaphthyl)sulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; monophenyldimethylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; diphenylmonomethylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; (4-methylphenyl)diphenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; (4-methoxyphenyl)diphenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; tri(4-tert-butyl)phenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; diphenyl (1-(4-methoxy)naphthyl)sulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; di(1-naphthyl)phenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-phenyltetrahydrothiophenium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-(4-methylphenyl)tetrahydrothiophenium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiophenium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-(4-methoxynaphthalene-1-yl)tetrahydrothiophenium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-(4-ethoxynaphthalene-1-yl)tetrahydrothiophenium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-(4-n-butoxynaphthalene-1-yl)tetrahydrothiophenium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-phenyltetrahydrothiopyranium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-(4-hydroxyphenyl)tetrahydrothiopyranium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiopyranium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; and 1-(4-methylphenyl)tetrahydrothiopyranium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate.

It is also possible to use each of onium salts in which the anion moiety of these onium salts is replaced by an alkyl sulfonate, such as methanesulfonate, n-propanesulfonate, n-butanesulfonate, n-octanesulfonate, 1-adamantanesulfonate or 2-norbornanesulfonate; or replaced by a sulfonate, such as d-camphor-10-sulfonate, benzenesulfonate, perfluorobenzenesulfonate or p-toluenesulfonate.

Furthermore, onium salts in which the anion moiety of these onium salts are replaced by an anion represented by any one of formulas (b1) to (b8) shown below can be used.

In the formulas, y represents an integer of 1 to 3; each of q1 and q2 independently represents an integer of 1 to 5; q3 represents an integer of 1 to 12; t3 represents an integer of 1 to 3; each of r1 and r2 independently represents an integer of 0 to 3; i represents an integer of 1 to 20; R⁵⁰ represents a substituent; each of m1 to m5 independently represents 0 or 1; each of v0 to v5 independently represents an integer of 0 to 3; each of w1 to w5 independently represents an integer of 0 to 3; and Q″ is the same as defined above.

As the substituent for R⁵⁰, the same groups as those which the aforementioned aliphatic hydrocarbon group or aromatic hydrocarbon group for R^(X) may have as a substituent can be used.

If there are two or more of the R⁵⁰ group, as indicated by the values r1, r2, and w1 to w5, then the two or more of the R⁵⁰ groups may be the same or different from each other.

Further, onium salt-based acid generators in which the anion moiety (R⁴″SO₃ ⁻) in general formula (b-1) or (b-2) is replaced by an anion moiety represented by general formula (b-3) or (b-4) shown below (the cation moiety is the same cation moiety as the aforementioned formula (b-1) or (b-2)) may be used.

In the formulas, X″ represents an alkylene group of 2 to 6 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom; and each of Y″ and Z″ independently represents an alkyl group of 1 to 10 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom.

X″ represents a linear or branched alkylene group in which at least one hydrogen atom has been substituted with a fluorine atom, and the alkylene group has 2 to 6 carbon atoms, preferably 3 to 5 carbon atoms, and most preferably 3 carbon atoms.

Each of Y″ and Z″ independently represents a linear or branched alkyl group in which at least one hydrogen atom has been substituted with a fluorine atom, and the alkyl group has 1 to 10 carbon atoms, preferably 1 to 7 carbon atoms, and most preferably 1 to 3 carbon atoms.

The smaller the number of carbon atoms of the alkylene group for X″ or those of the alkyl group for Y″ and Z″ within the above-mentioned range of the number of carbon atoms, the more the solubility in a resist solvent is improved.

Further, in the alkylene group for X″ or the alkyl group for Y″ and Z″, it is preferable that the number of hydrogen atoms substituted with fluorine atoms be as large as possible because the acid strength increases and the transparency to high energy radiation of 200 nm or less or electron beam is improved.

The fluorination ratio of the alkylene group or alkyl group is preferably from 70 to 100%, more preferably from 90 to 100%, and it is particularly desirable that the alkylene group or alkyl group be a perfluoroalkylene group or perfluoroalkyl group in which all hydrogen atoms are substituted with fluorine atoms.

Further, an onium salt-based acid generator in which the anion moiety (R⁴″SO₃ ⁻) in general formula (b-1) or (b-2) has been replaced with R^(h)—COO⁻ (in the formula, R^(h) represents an alkyl group or a fluorinated alkyl group) can also be used as the onium salt-based acid generator (the cation moiety is the same as that in general formula (b-1) or (b-2)).

In the formula above, as R^(h), the same groups as those described above for R⁴″ can be used.

Specific examples of the group represented by the formula “R^(h)—COO⁻” include a trifluoroacetic acid ion, an acetic acid ion, and a 1-adamantanecarboxylic acid ion.

Furthermore, as an onium salt-based acid generator, a sulfonium salt having a cation represented by general formula (b-5) or (b-6) shown below in a cation moiety may be used.

In formulas (b-5) and (b-6) above, each of R⁸¹ to R⁸⁶ independently represents an alkyl group, an acetyl group, an alkoxy group, a carboxy group, a hydroxyl group or a hydroxyalkyl group; each of n₁ to n₅ independently represents an integer of 0 to 3; and n₆ represents an integer of 0 to 2.

With respect to R⁸¹ to R⁸⁶, the alkyl group is preferably an alkyl group of 1 to 5 carbon atoms, more preferably a linear or branched alkyl group, and most preferably a methyl group, ethyl group, propyl group, isopropyl group, n-butyl group or tert-butyl group.

The alkoxy group is preferably an alkoxy group of 1 to 5 carbon atoms, more preferably a linear or branched alkoxy group, and most preferably a methoxy group or ethoxy group.

The hydroxyalkyl group is preferably the aforementioned alkyl group in which one or more hydrogen atoms have been substituted with hydroxy groups, and examples thereof include a hydroxymethyl group, a hydroxyethyl group and a hydroxypropyl group.

If there are two or more of an individual R⁸¹ to R⁸⁶ group, as indicated by the corresponding value of n₁ to n₆, then the two or more of the individual R⁸¹ to R⁸⁶ group may be the same or different from each other.

n₁ is preferably 0 to 2, more preferably 0 or 1, and still more preferably 0.

It is preferable that n₂ and n₃ each independently represents 0 or 1, and more preferably 0.

n₄ is preferably 0 to 2, and more preferably 0 or 1.

n₅ is preferably 0 or 1, and more preferably 0.

n₆ is preferably 0 or 1, and more preferably 1.

Preferable examples of the cation represented by formula (b-5) or (b-6) include the following.

Further, the sulfonium salt having a cation represented by general formula (b-7) or (b-8) shown below in a cation moiety can also be used.

In formulas (b-7) and (b-8), each of R⁹ and R¹⁰ independently represents a phenyl group or naphthyl group which may have a substituent, an alkyl group of 1 to 5 carbon atoms, an alkoxy group or a hydroxy group. Examples of the substituent are the same as the substituents described above in relation to the substituted aryl group for R¹″ to R³″ (i.e., an alkyl group, an alkoxy group, an alkoxyalkyloxy group, an alkoxycarbonylalkyloxy group, a halogen atom, a hydroxy group, an oxo group (═O), an aryl group, —C(═O)—O—R⁶′, —O—C(═O)—R⁷′, —O—R⁸′, a group in which R⁵⁶′ in the aforementioned general formula —O—R⁵⁰—C(═O)—O—R⁵⁶ has been substituted with R⁵⁶′).

R⁴′ represents an alkylene group of 1 to 5 carbon atoms.

u is an integer of 1 to 3, and most preferably 1 or 2.

Preferable examples of the cation represented by formula (b-7) or (b-8) are shown below. In the formulas, R^(C) represents the same substituents described above in relation to the aforementioned substituted aryl group (i.e., an alkyl group, an alkoxy group, an alkoxyalkyloxy group, an alkoxycarbonylalkyloxy group, a halogen atom, a hydroxy group, an oxo group (═O), an aryl group, —C(═O)—O—R⁶′, —O—C(═O)—R⁷′, —O—R⁸′).

The anion moiety of the sulfonium salt having a cation represented by general formula (b-5) to (b-8) in a cation moiety is not particularly limited, and the same anion moieties for onium salt-based acid generators which have been proposed may be used. Examples of such anion moieties include fluorinated alkylsulfonic acid ions such as anion moieties (R⁴″SO₃ ⁻) for onium salt-based acid generators represented by general formula (b-1) or (b-2) shown above; and anions represented by general formula (b-3) or (b-4) shown above, or an anion represented by any one of the aforementioned formulas (b1) to (b8).

In the present description, an oximesulfonate-based acid generator is a compound having at least one group represented by general formula (B-1) shown below, and has a feature of generating acid by irradiation (exposure). Such oximesulfonate acid generators are widely used for a chemically amplified resist composition, and can be appropriately selected.

In formula (B-1), each of R³¹ and R³² independently represents an organic group.

The organic group for R³¹ and R³² refers to a group containing a carbon atom, and may include atoms other than carbon atoms (e.g., a hydrogen atom, an oxygen atom, a nitrogen atom, a sulfur atom, a halogen atom (such as a fluorine atom and a chlorine atom) and the like).

As the organic group for R³¹, a linear, branched, or cyclic alkyl group or aryl group is preferable. The alkyl group or the aryl group may have a substituent. The substituent is not particularly limited, and examples thereof include a fluorine atom and a linear, branched, or cyclic alkyl group having 1 to 6 carbon atoms. The alkyl group or the aryl group “has a substituent” means that part or all of the hydrogen atoms of the alkyl group or the aryl group are substituted with a substituent.

The alkyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 10 carbon atoms, still more preferably 1 to 8 carbon atoms, still more preferably 1 to 6 carbon atoms, and most preferably 1 to 4 carbon atoms. As the alkyl group, a partially or completely halogenated alkyl group (hereinafter, sometimes referred to as a “halogenated alkyl group”) is particularly desirable. The “partially halogenated alkyl group” refers to an alkyl group in which part of the hydrogen atoms are substituted with halogen atoms and the “completely halogenated alkyl group” refers to an alkyl group in which all of the hydrogen atoms are substituted with halogen atoms. Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms and iodine atoms, and fluorine atoms are particularly desirable. In other words, the halogenated alkyl group is preferably a fluorinated alkyl group.

The aryl group preferably has 4 to 20 carbon atoms, more preferably 4 to 10 carbon atoms, and most preferably 6 to 10 carbon atoms. As the aryl group, partially or completely halogenated aryl group is particularly desirable. The “partially halogenated aryl group” refers to an aryl group in which some of the hydrogen atoms are substituted with halogen atoms and the “completely halogenated aryl group” refers to an aryl group in which all of hydrogen atoms are substituted with halogen atoms.

As R³¹, an alkyl group of 1 to 4 carbon atoms which has no substituent or a fluorinated alkyl group of 1 to 4 carbon atoms is particularly desirable.

As the organic group for R³², a linear, branched, or cyclic alkyl group, aryl group, or cyano group is preferable. Examples of the alkyl group and the aryl group for R³² include the same alkyl groups and aryl groups as those described above for R³¹.

As R³², a cyano group, an alkyl group of 1 to 8 carbon atoms having no substituent or a fluorinated alkyl group of 1 to 8 carbon atoms is particularly desirable.

Preferred examples of the oxime sulfonate acid generator include compounds represented by general formula (B-2) or (B-3) shown below.

In the formula, R³³ represents a cyano group, an alkyl group having no substituent or a halogenated alkyl group; R³⁴ represents an aryl group; and R³⁵ represents an alkyl group having no substituent or a halogenated alkyl group.

In the formula, R³⁶ represents a cyano group, an alkyl group having no substituent or a halogenated alkyl group; R³⁷ represents a divalent or trivalent aromatic hydrocarbon group; R³⁸ represents an alkyl group having no substituent or a halogenated alkyl group; and p″ represents 2 or 3.

In general formula (B-2), the alkyl group having no substituent or the halogenated alkyl group for R³³ preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 6 carbon atoms.

As R³³, a halogenated alkyl group is preferable, and a fluorinated alkyl group is more preferable.

The fluorinated alkyl group for R³³ preferably has 50% or more of the hydrogen atoms thereof fluorinated, more preferably 70% or more, and most preferably 90% or more.

Examples of the aryl group for R³⁴ include groups in which one hydrogen atom has been removed from an aromatic hydrocarbon ring, such as a phenyl group, a biphenyl group, a fluorenyl group, a naphthyl group, an anthryl group, and a phenanthryl group, and heteroaryl groups in which some of the carbon atoms constituting the ring(s) of these groups are substituted with heteroatoms such as an oxygen atom, a sulfur atom, and a nitrogen atom. Of these, a fluorenyl group is preferable.

The aryl group for R³⁴ may have a substituent such as an alkyl group of 1 to 10 carbon atoms, a halogenated alkyl group, or an alkoxy group. The alkyl group and halogenated alkyl group as the substituent preferably has 1 to 8 carbon atoms, and more preferably 1 to 4 carbon atoms. Further, the halogenated alkyl group is preferably a fluorinated alkyl group.

The alkyl group having no substituent or the halogenated alkyl group for R³⁵ preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 6 carbon atoms.

As R³⁵, a halogenated alkyl group is preferable, and a fluorinated alkyl group is more preferable.

In terms of enhancing the strength of the acid generated, the fluorinated alkyl group for R³⁵ preferably has 50% or more of the hydrogen atoms fluorinated, more preferably 70% or more, still more preferably 90% or more. A completely fluorinated alkyl group in which 100% of the hydrogen atoms are substituted with fluorine atoms is particularly desirable.

In general formula (B-3), as the alkyl group having no substituent and the halogenated alkyl group for R³⁶, the same alkyl group having no substituent and the halogenated alkyl group described above for R³³ can be used.

Examples of the divalent or trivalent aromatic hydrocarbon group for R³⁷ include groups in which one or two hydrogen atoms have been removed from the aryl group for R³⁴.

As the alkyl group having no substituent or the halogenated alkyl group for R³⁸, the same one as the alkyl group having no substituent or the halogenated alkyl group for R³⁵ can be used.

p″ is preferably 2.

Specific examples of suitable oxime sulfonate acid generators include α-(p-toluenesulfonyloxyimino)-benzyl cyanide, α-(p-chlorobenzenesulfonyloxyimino)-benzyl cyanide, α-(4-nitrobenzenesulfonyloxyimino)-benzyl cyanide, α-(4-nitro-2-trifluoromethylbenzenesulfonyloxyimino)-benzyl cyanide, α-(benzenesulfonyloxyimino)-4-chlorobenzyl cyanide, α-(benzenesulfonyloxyimino)-2,4-dichlorobenzyl cyanide, α-(benzenesulfonyloxyimino)-2,6-dichlorobenzyl cyanide, α-(benzenesulfonyloxyimino)-4-methoxybenzyl cyanide, α-(2-chlorobenzenesulfonyloxyimino)-4-methoxybenzyl cyanide, α-(benzenesulfonyloxyimino)-thien-2-yl acetonitrile, α-(4-dodecylbenzenesulfonyloxyimino)benzyl cyanide, α-[(p-toluenesulfonyloxyimino)-4-methoxyphenyl]acetonitrile, α-[(dodecylbenzenesulfonyloxyimino)-4-methoxyphenyl]acetonitrile, α-(tosyloxyimino)-4-thienyl cyanide, α-(methylsulfonyloxyimino)-1-cyclopentenyl acetonitrile, α-(methylsulfonyloxyimino)-1-cyclohexenyl acetonitrile, α-(methylsulfonyloxyimino)-1-cycloheptenyl acetonitrile, α-(methylsulfonyloxyimino)-1-cyclooctenyl acetonitrile, α-(trifluoromethylsulfonyloxyimino)-1-cyclopentenyl acetonitrile, α-(trifluoromethylsulfonyloxyimino)-cyclohexyl acetonitrile, α-(ethylsulfonyloxyimino)-ethyl acetonitrile, α-(propylsulfonyloxyimino)-propyl acetonitrile, α-(cyclohexylsulfonyloxyimino)-cyclopentyl acetonitrile, α-(cyclohexylsulfonyloxyimino)-cyclohexyl acetonitrile, α-(cyclohexylsulfonyloxyimino)-1-cyclopentenyl acetonitrile, α-(ethylsulfonyloxyimino)-1-cyclopentenyl acetonitrile, α-(isopropylsulfonyloxyimino)-1-cyclopentenyl acetonitrile, α-(n-butylsulfonyloxyimino)-1-cyclopentenyl acetonitrile, α-(ethylsulfonyloxyimino)-1-cyclohexenyl acetonitrile, α-(isopropylsulfonyloxyimino)-1-cyclohexenyl acetonitrile, α-(n-butylsulfonyloxyimino)-1-cyclohexenyl acetonitrile, α-(methylsulfonyloxyimino)-phenyl acetonitrile, α-(methylsulfonyloxyimino)-p-methoxyphenyl acetonitrile, α-(trifluoromethylsulfonyloxyimino)-phenyl acetonitrile, α-(trifluoromethylsulfonyloxyimino)-p-methoxyphenyl acetonitrile, α-(ethylsulfonyloxyimino)-p-methoxyphenyl acetonitrile, α-(propylsulfonyloxyimino)-p-methylphenyl acetonitrile, and α-(methylsulfonyloxyimino)-p-bromophenyl acetonitrile.

Further, oxime sulfonate acid generators disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 9-208554 (Chemical Formulas 18 and 19 shown in paragraphs [0012] to [0014]) and oxime sulfonate acid generators disclosed in WO 2004/074242A2 (Examples 1 to 40 described at pages 65 to 85) may be preferably used.

Furthermore, as preferable examples, the following can be used.

Of the aforementioned diazomethane acid generators, specific examples of suitable bisalkyl or bisaryl sulfonyl diazomethanes include bis(isopropylsulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane, bis(1,1-dimethylethylsulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane, and bis(2,4-dimethylphenylsulfonyl)diazomethane.

Further, diazomethane acid generators disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 11-035551, Japanese Unexamined Patent Application, First Publication No. Hei 11-035552 and Japanese Unexamined Patent Application, First Publication No. Hei 11-035573 may be preferably used.

Furthermore, as examples of poly(bis-sulfonyl)diazomethanes, those disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 11-322707, including 1,3-bis(phenylsulfonyldiazomethylsulfonyl)propane, 1,4-bis(phenylsulfonyldiazomethylsulfonyl)butane, 1,6-bis(phenylsulfonyldiazomethylsulfonyl)hexane, 1,10-bis(phenylsulfonyldiazomethylsulfonyl)decane, 1,2-bis(cyclohexylsulfonyldiazomethylsulfonyl)ethane, 1,3-bis(cyclohexylsulfonyldiazomethylsulfonyl)propane, 1,6-bis(cyclohexylsulfonyldiazomethylsulfonyl)hexane, and 1,10-bis(cyclohexylsulfonyldiazomethylsulfonyl)decane, may be given.

As the component (B), one type of acid generator described above may be used, or two or more types of the acid generators may be used in combination.

In the positive resist composition of the present invention, the amount of the component (B) relative to 100 parts by weight of the component (A) is preferably 0.5 to 60 parts by weight, more preferably 1 to 50 parts by weight, and still more preferably 1 to 40 parts by weight. When the amount of the component (B) is within the above-mentioned range, formation of a resist pattern can be satisfactorily performed. Further, when each component of the resist composition is dissolved in the organic solvent, by virtue of the above-mentioned range, a uniform solution can be obtained and the storage stability becomes satisfactory.

<Optional Components>

The resist composition of the present invention may include a nitrogen-containing organic compound (D) which does not fall under the category of the component (A) or (B) (hereafter referred to as the component (D)), as long as the effects of the present invention are not impaired.

As the component (D), there is no particular limitation as long as it functions as an acid diffusion control agent, i.e., a quencher which traps the acid generated from the component (B) upon exposure. A multitude of these components (D) have already been proposed, and any of these known compounds may be used. Examples of the component (D) include an aliphatic amine and an aromatic amine, although an aliphatic amine, and particularly a secondary aliphatic amine or tertiary aliphatic amine is preferable.

An aliphatic amine is an amine having one or more aliphatic groups, and the aliphatic groups preferably have 1 to 20 carbon atoms.

Examples of these aliphatic amines include amines in which at least one hydrogen atom of ammonia (NH₃) has been substituted with an alkyl group or hydroxyalkyl group of no more than 20 carbon atoms (i.e., alkylamines or alkylalcoholamines), and cyclic amines.

The alkyl group and the alkyl group for the hydroxyalkyl group may be any of linear, branched or cyclic.

When the alkyl group is linear or branched, the alkyl group preferably has 2 to 20 carbon atoms, and more preferably 2 to 8 carbon atoms.

When the alkyl group is cyclic (i.e., a cycloalkyl group), the number of carbon atoms is preferably 3 to 30, more preferably 3 to 20, still more preferably 3 to 15, still more preferably 4 to 12, and most preferably 5 to 10. The alkyl group may be monocyclic or polycyclic. Examples thereof include groups in which one or more of the hydrogen atoms have been removed from a monocycloalkane; and groups in which one or more of the hydrogen atoms have been removed from a polycycloalkane such as a bicycloalkane, a tricycloalkane, or a tetracycloalkane. Specific examples of the monocycloalkane include cyclopentane and cyclohexane. Specific examples of the polycycloalkane include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane.

Specific examples of the alkylamines include monoalkylamines such as n-hexylamine, n-heptylamine, n-octylamine, n-nonylamine, and n-decylamine; dialkylamines such as diethylamine, di-n-propylamine, di-n-heptylamine, di-n-octylamine, and dicyclohexylamine; and trialkylamines such as trimethylamine, triethylamine, tri-n-propylamine, tri-n-butylamine, tri-n-hexylamine, tri-n-pentylamine, tri-n-heptylamine, tri-n-octylamine, tri-n-nonylamine, tri-n-decylamine, and tri-n-dodecylamine.

Specific examples of the alkylalcoholamines include diethanolamine, triethanolamine, diisopropanolamine, triisopropanolamine, di-n-octanolamine, tri-n-octanolamine, stearyldiethanolamine and laurildiethanolamine.

Examples of the cyclic amine include heterocyclic compounds containing a nitrogen atom as a heteroatom. The heterocyclic compound may be a monocyclic compound (aliphatic monocyclic amine), or a polycyclic compound (aliphatic polycyclic amine).

Specific examples of the aliphatic monocyclic amine include piperidine, and piperazine.

The aliphatic polycyclic amine preferably has 6 to 10 carbon atoms, and specific examples thereof include 1,5-diazabicyclo[4.3.0]-5-nonene, 1,8-diazabicyclo[5.4.0]-7-undecene, hexamethylenetetramine, and 1,4-diazabicyclo[2.2.2]octane.

Examples of other aliphatic amines include tris(2-methoxymethoxyethyl)amine, tris{2-(2-methoxyethoxy)ethyl}amine, tris{2-(2-methoxyethoxymethoxy)ethyl}amine, tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine, tris{2-(1-ethoxypropoxy)ethyl}amine and tris[2-{2-(2-hydroxyethoxy)ethoxy}ethyl]amine.

Examples of aromatic amines include aniline, pyridine, 4-dimethylaminopyridine, pyrrole, indole, pyrazole, imidazole and derivatives thereof, as well as diphenylamine, triphenylamine and tribenzylamine.

These compounds can be used either alone, or in combinations of two or more different compounds.

The component (D) is typically used in an amount within a range from 0.01 to 5.0 parts by weight, relative to 100 parts by weight of the component (A). When the amount of the component (D) is within the above-mentioned range, the shape of the resist pattern and the post exposure stability of the latent image formed by the pattern-wise exposure of the resist layer are improved.

Furthermore, in the resist composition of the present invention, for preventing any deterioration in sensitivity, and improving the resist pattern shape and the post exposure stability of the latent image formed by the pattern-wise exposure of the resist layer, at least one compound (E) (hereafter referred to as “the component (E)”) selected from the group consisting of an organic carboxylic acid, or a phosphorus oxo acid or derivative thereof can be added.

Examples of suitable organic carboxylic acids include acetic acid, malonic acid, citric acid, malic acid, succinic acid, benzoic acid, and salicylic acid.

Examples of phosphorus oxo acids include phosphoric acid, phosphonic acid and phosphinic acid. Among these, phosphonic acid is particularly desirable.

Examples of oxo acid derivatives include esters in which a hydrogen atom within the above-mentioned oxo acids is substituted with a hydrocarbon group. Examples of the hydrocarbon group include an alkyl group of 1 to 5 carbon atoms and an aryl group of 6 to 15 carbon atoms.

Examples of phosphoric acid derivatives include phosphoric acid esters such as di-n-butyl phosphate and diphenyl phosphate.

Examples of phosphonic acid derivatives include phosphonic acid esters such as dimethyl phosphonate, di-n-butyl phosphonate, phenylphosphonic acid, diphenyl phosphonate and dibenzyl phosphonate.

Examples of phosphinic acid derivatives include phosphinic acid esters such as phenylphosphinic acid.

As the component (E), one type may be used alone, or two or more types may be used in combination.

The component (E) is typically used in an amount within a range from 0.01 to 5.0 parts by weight, relative to 100 parts by weight of the component (A).

If desired, miscible additives can also be added to the resist composition of the present invention. Examples of such miscible additives include additive resins for improving the performance of the resist film, surfactants for improving the applicability, dissolution inhibitors, plasticizers, stabilizers, colorants, halation prevention agents, and dyes.

The resist composition of the present invention can be prepared by dissolving the materials for the resist composition in an organic solvent (hereafter, frequently referred to as “component (S)”).

The component (S) may be any organic solvent which can dissolve the respective components to give a uniform solution, and one or more kinds of any organic solvent can be appropriately selected from those which have been conventionally known as solvents for a chemically amplified resist.

Examples thereof include lactones such as γ-butyrolactone;

ketones such as acetone, methyl ethyl ketone, cyclohexanone, methyl-n-pentyl ketone, methyl isopentyl ketone, and 2-heptanone;

polyhydric alcohols, such as ethylene glycol, diethylene glycol, propylene glycol and dipropylene glycol;

compounds having an ester bond, such as ethylene glycol monoacetate, diethylene glycol monoacetate, propylene glycol monoacetate, and dipropylene glycol monoacetate;

polyhydric alcohol derivatives including compounds having an ether bond, such as a monoalkylether (e.g., monomethylether, monoethylether, monopropylether or monobutylether) or monophenylether of any of these polyhydric alcohols or compounds having an ester bond (among these, propylene glycol monomethyl ether acetate (PGMEA) and propylene glycol monomethyl ether (PGME) are preferable); cyclic ethers such as dioxane; esters such as methyl lactate, ethyl lactate (EL), methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, and ethyl ethoxypropionate; and aromatic organic solvents such as anisole, ethylbenzylether, cresylmethylether, diphenylether, dibenzylether, phenetole, butylphenylether, ethylbenzene, diethylbenzene, pentylbenzene, isopropylbenzene, toluene, xylene, cymene and mesitylene.

These solvents can be used individually, or in combination as a mixed solvent.

Among these, propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monomethyl ether (PGME), cyclohexanone and ethyl lactate (EL) are preferable.

Further, among the mixed solvents, a mixed solvent obtained by mixing PGMEA with a polar solvent is preferable. The mixing ratio (weight ratio) of the mixed solvent can be appropriately determined, taking into consideration the compatibility of the PGMEA with the polar solvent, but is preferably in the range of 1:9 to 9:1, more preferably from 2:8 to 8:2. For example, when EL is mixed as the polar solvent, the PGMEA:EL weight ratio is preferably from 1:9 to 9:1, and more preferably from 2:8 to 8:2. Alternatively, when PGME is mixed as the polar solvent, the PGMEA:PGME weight ratio is preferably from 1:9 to 9:1, more preferably from 2:8 to 8:2, and still more preferably 3:7 to 7:3. Alternatively, when PGME and cyclohexanone is mixed as the polar solvent, the PGMEA:PGME and cyclohexanone weight ratio is preferably from 1:9 to 9:1, more preferably from 2:8 to 8:2, and still more preferably 3:7 to 7:3.

Further, as the component (S), a mixed solvent of one of PGMEA, EL, or the mixed solvent of PGMEA and the polar solvent with γ-butyrolactone is also preferable. The mixing ratio (former:latter) of such a mixed solvent is preferably from 70:30 to 95:5.

The amount of the organic solvent is not particularly limited, and is appropriately adjusted to a concentration which enables coating of a coating solution to a substrate, depending on the thickness of the coating film. In general, the organic solvent is used in an amount such that the solid content of the resist composition becomes within the range from 1 to 20% by weight, and preferably from 2 to 15% by weight.

The resist composition of the present invention exhibits excellent lithography properties such as exposure latitude (EL), roughness of the line width (line width roughness (LWR)) and the like and enables formation of a resist pattern having an excellent shape.

In the present invention, the reasons why such effects can be achieved have not been elucidated yet. However, since the component (A1) represents a polymeric compound, the structural unit (a5) constituting the component (A1) and having the structure —N(R^(a))—C(═O)—R^(b) on the side chain thereof can readily be uniformly distributed within the resist film. Therefore, during the formation of a resist pattern, a quenching effect in which the acid generated from the component (B) in the exposed portions of the resist film is trapped can readily be uniformly obtained in the entire resist film. As a result, it is presumed that since changing solubility of the component (A) at unexposed portions in a developing solution can be suppressed, such effects can be achieved.

In addition, the component (A1) exhibits high solubility in solvents for a chemically amplified resist, and exhibits excellent solubility in propylene glycol monomethyl ether (PGME). As a result, according to a resist composition containing the component (A1), generation of defects by developing can be suppressed.

It is presumed that since the component (A1) includes the structural unit (a5) having an imide group on the side chain thereof, the compatibility thereof with the solvent can be increased.

<<Method of Forming a Resist Pattern>>

The method of forming a resist pattern according to the present invention described above includes: forming a resist film on a substrate using a resist composition of the present invention; conducting exposure of the resist film; and developing the resist film to form a resist pattern.

The method for forming a resist pattern according to the present invention can be performed, for example, as follows.

Firstly, the resist composition of the present invention is applied to a substrate using a spinner or the like, and a bake treatment (post applied bake (PAB)) is conducted at a temperature of 80 to 150° C. for 40 to 120 seconds, preferably 60 to 90 seconds, to form a resist film.

Following selective exposure of the thus formed resist film, either by exposure through a mask having a predetermined pattern formed thereon (mask pattern) using an exposure apparatus such as an ArF exposure apparatus, an electron beam lithography apparatus or an EUV exposure apparatus, or by patterning via direct irradiation with an electron beam without using a mask pattern, baking treatment (post exposure baking (PEB)) is conducted under temperature conditions of 80 to 150° C. for 40 to 120 seconds, and preferably 60 to 90 seconds.

Subsequently, the resulting resist film is subjected to developing treatment.

For an alkali developing process, an alkali developing solution is used in developing treatment. For a solvent developing process, a developing solution containing an organic solvent (organic developing solution) is used in developing treatment.

After the developing treatment, it is preferable to perform rinse treatment. In the case of an alkali developing process, the rinse treatment is preferably a water rinse using pure water. In the case of a solvent developing process, it is preferable to use a rinse liquid containing an organic solvent.

In the case of a solvent developing process, after the developing treatment or the rinse treatment, the developing solution or the rinse liquid remaining on the pattern can be removed by a treatment using a supercritical fluid.

After the developing treatment or the rinse treatment, drying is conducted. If desired, bake treatment (post bake) can be conducted following the developing. In this manner, a resist pattern can be obtained.

The substrate is not specifically limited and a conventionally known substrate can be used. For example, substrates for electronic components, and such substrates having wiring patterns formed thereon can be used. Specific examples of the material of the substrate include metals such as silicon wafer, copper, chromium, iron and aluminum; and glass. Suitable materials for the wiring pattern include copper, aluminum, nickel, and gold.

Further, as the substrate, any one of the above-mentioned substrates provided with an inorganic and/or organic film on the surface thereof may be used. As the inorganic film, an inorganic antireflection film (inorganic BARC) can be used. As the organic film, an organic antireflection film (organic BARC) and an organic film such as a lower-layer organic film used in a multilayer resist method can be used.

Here, a “multilayer resist method” is a method in which at least one layer of an organic film (lower-layer organic film) and at least one layer of a resist film (upper resist film) are provided on a substrate, and a resist pattern formed on the upper resist film is used as a mask to conduct patterning of the lower-layer organic film. This method is considered as being capable of forming a pattern with a high aspect ratio. More specifically, in the multilayer resist method, a desired thickness can be ensured by the lower-layer organic film, and as a result, the thickness of the resist film can be reduced, and an extremely fine pattern with a high aspect ratio can be formed.

The multilayer resist method is broadly classified into a method in which a double-layer structure consisting of an upper-layer resist film and a lower-layer organic film is formed (double-layer resist method), and a method in which a multilayer structure having at least three layers consisting of an upper-layer resist film, a lower-layer organic film and at least one intermediate layer (thin metal film or the like) provided between the upper-layer resist film and the lower-layer organic film (triple-layer resist method).

The wavelength to be used for exposure is not particularly limited and the exposure can be conducted using radiation such as ArF excimer laser, KrF excimer laser, F₂ excimer laser, extreme ultraviolet rays (EUV), vacuum ultraviolet rays (VUV), electron beam (EB), X-rays, and soft X-rays. The resist composition of the present invention is effective to KrF excimer laser, ArF excimer laser, EB and EUV.

The exposure of the resist film can be either a general exposure (dry exposure) conducted in air or an inert gas such as nitrogen, or immersion exposure (immersion lithography).

In immersion lithography, the region between the resist film and the lens at the lowermost point of the exposure apparatus is pre-filled with a solvent (immersion medium) that has a larger refractive index than the refractive index of air, and the exposure (immersion exposure) is conducted in this state.

The immersion medium preferably exhibits a refractive index larger than the refractive index of air but smaller than the refractive index of the resist film to be exposed. The refractive index of the immersion medium is not particularly limited as long at it satisfies the above-mentioned requirements.

Examples of this immersion medium which exhibits a refractive index that is larger than the refractive index of air but smaller than the refractive index of the resist film include water, fluorine-based inert liquids, silicon-based solvents and hydrocarbon-based solvents.

Specific examples of the fluorine-based inert liquids include liquids containing a fluorine-based compound such as C₃HCl₂F₅, C₄F₉OCH₃, C₄F₉OC₂H₅ or C₅H₃F₇ as the main component, which have a boiling point within a range from 70 to 180° C. and preferably from 80 to 160° C. A fluorine-based inert liquid having a boiling point within the above-mentioned range is advantageous in that the removal of the immersion medium after the exposure can be conducted by a simple method.

As a fluorine-based inert liquid, a perfluoroalkyl compound in which all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms is particularly desirable. Examples of these perfluoroalkyl compounds include perfluoroalkylether compounds and perfluoroalkylamine compounds.

Specifically, one example of a suitable perfluoroalkylether compound is perfluoro (2-butyl-tetrahydrofuran) (boiling point 102° C.), and an example of a suitable perfluoroalkylamine compound is perfluorotributylamine (boiling point 174° C.).

As the immersion medium, water is preferable in terms of cost, safety, environment and versatility.

As examples of the alkali developing solution for developing treatment in an alkali developing process, a 0.1 to 10% by weight aqueous solution of tetramethylammonium hydroxide (TMAH) can be given.

As the organic solvent contained in the organic developing solution for developing treatment in a solvent developing process, any of the conventional organic solvents can be used which are capable of dissolving the component (A) (prior to exposure). Specific examples of the organic solvent include polar solvents such as ketone solvents, ester solvents, alcohol solvents, amide solvents and ether solvents, and hydrocarbon solvents.

If desired, the organic developing solution may have a conventional additive blended. Examples of the additive include surfactants. The surfactant is not particularly limited, and for example, an ionic or non-ionic fluorine and/or silicon surfactant can be used.

When a surfactant is added, the amount thereof based on the total amount of the organic developing solution is generally 0.001 to 5% by weight, preferably 0.005 to 2% by weight, and more preferably 0.01 to 0.5% by weight.

The development treatment can be performed by a conventional developing method. Examples thereof include a method in which the substrate is immersed in the developing solution for a predetermined time (a dip method), a method in which the developing solution is cast up on the surface of the substrate by surface tension and maintained for a predetermined period (a puddle method), a method in which the developing solution is sprayed onto the surface of the substrate (spray method), and a method in which the developing solution is continuously ejected from a developing solution ejecting nozzle while scanning at a constant rate to apply the developing solution to the substrate while rotating the substrate at a constant rate (dynamic dispense method).

As the organic solvent contained in the rinse liquid used for rinse treatment after the developing treatment in a solvent developing process, any of the aforementioned organic solvents for the organic developing solution can be used which hardly dissolve the pattern. In general, at least one solvent selected from the group consisting of hydrocarbon solvents, ketone solvents, ester solvents, alcohol solvents, amide solvents and ether solvents is used. Among these, at least one solvent selected from the group consisting of hydrocarbon solvents, ketone solvents, ester solvents, alcohol solvents and amide solvents is preferable, more preferably at least one solvent selected from the group consisting of alcohol solvents and ester solvents, and an alcohol solvent is particularly desirable.

The rinse treatment (washing treatment) using the rinse liquid can be performed by a conventional rinse method. Examples thereof include a method in which the rinse liquid is continuously applied to the substrate while rotating it at a constant rate (rotational coating method), a method in which the substrate is immersed in the rinse liquid for a predetermined time (dip method), and a method in which the rinse liquid is sprayed onto the surface of the substrate (spray method).

<<Polymeric Compound>>

The polymeric compound of the present invention includes a structural unit (a5) represented by general formula (a5-1) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; each of R^(a) and R^(b) independently represents a hydrocarbon group which may have a substituent, and R^(a) and R^(b) may be mutually bonded to form a ring.

Preferable examples of the structural unit (a5) include structural units represented by general formula (a5-1-1) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; X represents CH₂, CH₂CH₂, O, S or SO₂; each of R^(c) and R^(d) independently represents a hydrocarbon group which may have a substituent or a hydrogen atom, and R^(c) and R^(d) may be mutually bonded to form a ring; p represents an integer of 0 to 3.

The polymeric compound of the present invention preferably has, in addition to the structural unit (a5), a structural unit (a1) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and containing an acid decomposable group which exhibits increased polarity by the action of acid.

Further, the polymeric compound of the present invention preferably includes, in addition to the structural unit (a5) and the structural unit (a1), at least one structural unit selected from the group consisting of a structural unit (a0) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an —SO₂— containing cyclic group and a structural unit (a2) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains a lactone-containing cyclic group.

Furthermore, it is preferable that the polymeric compound of the present invention include a structural unit (a3) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains a polar group-containing aliphatic hydrocarbon group and, as well as the structural unit (a5) and the structural unit (a1), or the structural unit (a5), the structural unit (a1) and at least one structural unit selected from the group consisting of the structural unit (a0) and the structural unit (a2).

The explanation of the polymeric compound of the present invention is the same as the explanation of the component (A1) of the resist composition of the present invention described above.

EXAMPLES

A description of examples of the present invention follows, although the scope of the present invention is by no way limited by these examples.

In the following examples, a unit represented by a chemical formula (1) is referred to as “compound (1)”, and the same applies for compounds represented by other formulas.

In the NMR analysis, the internal standard for ¹H-NMR and ¹³C-NMR was tetramethylsilane (TMS). The internal standard for ¹⁹F-NMR was hexafluorobenzene (provided that the peak of hexafluorobenzene was regarded as −160 ppm).

Monomer Synthesis Example 1 Synthesis of Compound (6)

The compound (6) used in the polymer synthesis examples described later was synthesized as follows.

300 mL of a THF solution containing 20 g (105.14 mmol) of an alcohol (6), 30.23 g (157.71 mmol) of ethyldiisopropylaminocarbodiimide (EDCI) hydrochloride and 0.6 g (5 mmol) of dimethylaminopyridine (DMAP) was added to a 500 mL three-necked flask in a nitrogen atmosphere, and 16.67 g (115.66 mmol) of a precursor (6) was added thereto while cooling with ice (0° C.), followed by stirring at room temperature for 12 hours.

After conducting thin-layer chromatography (TLC) to confirm that the raw materials had dissipated, 50 mL of water was added to stop the reaction. Then, the reaction solvent was concentrated under reduced pressure, and extraction was conducted with ethyl acetate three times. The obtained organic phase was washed with water, saturated sodium hydrogencarbonate and 1N—HClaq in this order. Thereafter, the solvent was distilled off under reduced pressure, and the resulting product was dried, thereby obtaining the compound (6).

The results of NMR analysis of the obtained compound (6) were as follows.

¹H-NMR (CDCl₃, 400 MHz): δ(ppm)=6.22 (s, 1H, H^(a)), 5.70 (s, 1H, H^(b)), 4.71-4.85 (m, 2H, H^(c,d)), 4.67 (s, 2H, H^(k)), 3.40-3.60 (m, 2H, H^(e,f)), 2.58-2.70 (m, 1H, H^(g)), 2.11-2.21 (m, 2H, H^(h)), 2.00 (s, 3H, H^(i)), 1.76-2.09 (m, 2H, H^(j)).

Polymer Synthesis Example 1 Synthesis of Polymeric Compound 1

In a separable flask equipped with a thermometer, a reflux tube and a nitrogen feeding pipe, 12.00 g (70.52 mmol) of the compound (1), 9.97 g (40.63 mmol) of a compound (2), 17.88 g (68.13 mmol) of a compound (3), 5.63 g (33.47 mmol) of a compound (4) and 6.21 g (26.32 mmol) of a compound (5) were dissolved in 66.42 g of methyl ethyl ketone (MEK) to obtain a solution. Then, 11.95 mmol of dimethyl 2,2′-azobis(isobutyrate) (V-601) was added and dissolved in the obtained solution.

The resultant was dropwise added to 36.03 g of MEK heated to 80° C. in a nitrogen atmosphere over 3 hours. Thereafter, the reaction solution was heated for 2 hour while stirring, and then cooled to room temperature.

The obtained reaction polymer solution was dropwise added to an excess amount of a mixed solvent of n-heptane/isopropanol=90/10 (weight ratio), and an operation to deposit a polymer was conducted. Thereafter, the precipitated white powder was separated by filtration, followed by washing with a methanol and drying, thereby obtaining 32.49 g of a polymeric compound 1 as an objective compound.

With respect to the polymeric compound 1, the weight average molecular weight (Mw) and the dispersity (Mw/Mn) were determined by the polystyrene equivalent value as measured by gel permeation chromatography (GPC). As a result, it was found that the weight average molecular weight was 6,700, and the dispersity was 1.56.

Further, as a result of an analysis by carbon 13 nuclear magnetic resonance spectroscopy (600 MHz, ¹³C-NMR), it was found that the composition of the copolymer (ratio (molar ratio) of the respective structural units within the structural formula) was l/m/n/o/p=37.0/15.3/17.8/16.0/13.9.

Polymer Synthesis Examples 2 to 8 Synthesis of Polymeric Compounds 2 to 8

Polymeric compounds 2 to 8 were synthesized in the same manner as in Polymer Synthesis Example 1, except that the following compounds (1) to (8) which derived the structural units constituting each polymeric compound were used in predetermined molar ratio.

With respect to each polymeric compound, the compounds which derived each structural unit, the composition of the copolymer analyzed by carbon 13 nuclear magnetic resonance spectroscopy (600 MHz, ¹³C-NMR), the weight average molecular weight and the dispersity (Mw/Mn) determined by the polystyrene equivalent value as measured by gel permeation chromatography (GPC) are shown in Table 1.

TABLE 1 Compound which derived each Composition of Mw/ structural unit Copolymer Mw Mn Polymeric (1)/(2)/(3)/(4)/(5) 37.0/15.3/17.8/ 6700 1.56 Compound 1 16.0/13.9 Polymeric (6)/(3)/(2) 42.0/35.4/22.6 5600 1.52 Compound 2 Polymeric (2)/(3)/(7) 33.3/12.0/54.7 4600 1.58 Compound 3 Polymeric (2)/(3)/(8)/(5) 36.5/34.1/18.9/10.5 8200 1.61 Compound 4 Polymeric (1)/(6)/(3)/(4)/(5) 34.7/21.7/16.3/ 7900 1.57 Compound 5 14.8/12.5 Polymeric (6)/(3)/(5) 39.4/39.9/20.7 6000 1.42 Compound 6 Polymeric (6)/(3)/(7) 40.0/10.8/49.2 6100 1.61 Compound 7 Polymeric (6)/(3)/(8)/(5) 38.5/37.9/14.6/9.0 6400 1.55 Compound 8

Preparation of Resist Composition Examples 1 to 4, Comparative Examples 1 to 4

The components shown in Table 2 were mixed together and dissolved to obtain resist compositions.

TABLE 2 Com- Com- Com- Com- ponent ponent ponent ponent (A) Component (B) (D) (E) (S) Example 1 (A)-1 (B)-1 (B)-2 (D)-1 (E)-1 (S)-1 [100] [8.81] [3.11] [0.38] [0.47] [2700] Comparative (A)-2 (B)-1 (B)-2 (D)-1 (E)-1 (S)-1 Example 1 [100] [8.81] [3.11] [0.38] [0.47] [2700] Example 2 (A)-3 (B)-1 (B)-2 (D)-1 (E)-1 (S)-1 [100] [8.81] [3.11] [0.38] [0.47] [2700] Comparative (A)-4 (B)-1 (B)-2 (D)-1 (E)-1 (S)-1 Example 2 [100] [8.81] [3.11] [0.38] [0.47] [2700] Example 3 (A)-5 (B)-1 (B)-2 (D)-1 (E)-1 (S)-1 [100] [8.81] [3.11] [0.38] [0.47] [2700] Comparative (A)-6 (B)-1 (B)-2 (D)-1 (E)-1 (S)-1 Example 3 [100] [8.81] [3.11] [0.38] [0.47] [2700] Example 4 (A)-7 (B)-1 (B)-2 (D)-1 (E)-1 (S)-1 [100] [8.81] [3.11] [0.38] [0.47] [2700] Comparative (A)-8 (B)-1 (B)-2 (D)-1 (E)-1 (S)-1 Example 4 [100] [8.81] [3.11] [0.38] [0.47] [2700]

In Table 2, the values in brackets [ ] indicate the amount (in terms of parts by weight) of the component added. Further, the reference characters indicate the following.

(A)-1: the aforementioned polymeric compound 1

(A)-2: the aforementioned polymeric compound 5

(A)-3: the aforementioned polymeric compound 2

(A)-4: the aforementioned polymeric compound 6

(A)-5: the aforementioned polymeric compound 3

(A)-6: the aforementioned polymeric compound 7

(A)-7: the aforementioned polymeric compound 4

(A)-8: the aforementioned polymeric compound 8

(B)-1: a compound represented by chemical formula (B)-1 shown below

(B)-2: a compound represented by chemical formula (B)-2 shown below

(D)-1: tri-n-pentylamine

(E)-1: salicylic acid

(S)-1: a mixed solvent of PGMEA/PGME (60/40 by weight ratio)

<Formation of Resist Pattern>

An organic anti-reflection film composition (product name: ARC29, manufactured by Brewer Science Ltd.) was applied to an 8-inch silicon wafer using a spinner, and the composition was then baked at 205° C. for 60 seconds, thereby forming an organic anti-reflection film having a film thickness of 77 nm.

Then, each of the resist compositions obtained above was applied to the organic anti-reflection film using a spinner, and was then prebaked (PAB) on a hotplate at a PAB temperature indicated in Table 3 for 60 seconds and dried, thereby forming a resist film having a film thickness of 120 nm.

Subsequently, the resist film was selectively irradiated with an ArF excimer laser (193 nm) through a mask pattern (6% halftone mask), using an ArF exposure apparatus NSR-S302A (manufactured by Nikon Corporation, NA (numerical aperture)=0.60, 2/3 annular illumination).

Thereafter, a post exposure bake (PEB) treatment was conducted at a PAB temperature indicated in Table 3 for 60 seconds, followed by alkali development for 30 seconds at 23° C. in a 2.38% by weight aqueous solution of TMAH (product name: NMD-3; manufactured by Tokyo Ohka Kogyo Co., Ltd.). Then, the resist was washed for 30 seconds with pure water, further followed by conducting a bake treatment (post bake) at 100° C. for 60 seconds.

As a result, in each of the examples, a 1:1 line and space pattern (L/S pattern) having a line width of 130 nm and a pitch of 260 nm was formed on the resist film. The optimal exposure dose Eop (mJ/cm²) was determined. The results are shown in Table 3.

[Evaluation of Exposure Latitude (EL)]

With respect to the above Eop, the exposure dose with which an L/S pattern having a dimension of the target dimension (line width: 130 nm)±5% (i.e., 123.5 nm to 136.5 nm) was determined, and the EL (unit: %) was determined by the following formula. The results are shown in Table 3. EL(%)=(|E1−E2|/Eop)×100 In the formula, E1 represents the exposure dose (mJ/cm²) for forming an L/S pattern having a space width of 123.5 nm, and E2 represents the exposure dose (mJ/cm²) for forming an L/S pattern having a space width of 136.5 nm.

The larger the value of the “EL”, the smaller the change in the pattern size by the variation of the exposure dose.

[Evaluation of Line Width Roughness (LWR)]

With respect to each of the 1:1 L/S patterns, which have a line width of 130 nm and a pitch of 260 nm, formed with the above Eop, the space width at 5 points in the lengthwise direction of the space was measured using a measuring scanning electron microscope (SEM) (product name: S-9220, manufactured by Hitachi, Ltd.; acceleration voltage: 800V), and from the results, the value of 3 times the standard deviation s (i.e., 3 s) was calculated as a yardstick of LWR. The results are shown in Table 3.

The smaller this 3 s value is, the lower the level of roughness of the line width, indicating that an L/S pattern with a uniform width was obtained.

TABLE 3 PAB PEB Eop EL LWR (° C.) (° C.) (mJ/cm²) (%) (nm) Example 1 105 95 32.1 8.96 8.51 Comparative 105 95 22.2 8.54 10.75 Example 1 Example 2 100 90 31.5 7.39 8.23 Comparative 100 90 25.0 7.02 9.22 Example 2 Example 3 80 80 34.5 7.78 7.18 Comparative 80 80 27.1 6.34 8.49 Example 3 Example 4 80 80 37.4 8.44 7.44 Comparative 80 80 29.8 7.51 8.93 Example 4

From the results shown in Table 3, it was confirmed that the resist compositions of Examples 1 to 4 according to the present invention were superior to the resist compositions of Comparative Examples 1 to 4 corresponding to each of Examples 1 to 4 in that they exhibited excellent lithography properties and enabled formation of a resist pattern having an excellent shape, since the value of the EL thereof is larger and the value of the LWR thereof is small.

<Solubility of Base Component (A) in Organic Solvent>

Using polymeric compounds and organic solvents shown below, to become each solution in which the concentration of the polymeric compound is 1% by weight and 20% by weight, when each organic solvent was added to each polymeric compound and was mixed, it was evaluated whether each polymeric compound was dissolved in each organic solvent at room temperature (23° C.) or not.

Polymeric compound: the aforementioned polymeric compound 1 and the aforementioned polymeric compound 5

Organic solvent: propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether and cyclohexanone

The obtained evaluation results are shown in Table 4.

In Table, “A” indicates that the polymeric compound was dissolved as soon as mixing, “B” indicates that the polymeric compound was dissolved in long mixing time (for 30 minutes or more), “C” indicates that the polymeric compound was not dissolved, and “-” indicates no example.

TABLE 4 Polymeric Compound 5 Polymeric Compound 1 1% by 20% by 1% by 20% by Organic Solvent weight weight weight weight Propylene Glycol — B — A Monomethyl Ether Acetate Propylene Glycol C C — A Monomethyl Ether Cyclohexanone — A — A

From the results shown in Table 4, it was confirmed that the polymeric compound 1 of the present invention including a structural unit (a5) exhibited high solubility in each of the organic solvents.

While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims. 

What is claimed is:
 1. A resist composition comprising a base component (A) which exhibits changed solubility in a developing solution under action of acid and an acid-generator component (B) which generates acid upon exposure, wherein the base component (A) comprises a polymeric compound (A1) having a structural unit (a1) represented by general formula (a1-0-14), (a1-0-15) or (a1-0-2) shown below and a structural unit (a5) represented by general formula (a5-1-1) shown below:

wherein R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R²² represents a group which forms an aliphatic monocyclic group with the carbon atom to which R²² is bonded; R²⁴ represents a group which forms an aliphatic polycyclic group with the carbon atom to which R²⁴ is bonded; each of R¹⁵ and R¹⁶ independently represents an alkyl group; Y² represents a divalent linking group; and X² represents an acid dissociable group; and

wherein in formula (a5-1-1) R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; X represents CH₂, CH₂CH₂, O, S or SO₂; each of R^(c) and R^(d) independently represents a hydrocarbon group which may have a substituent or a hydrogen atom, and R^(c) and R^(d) may be mutually bonded to form a ring; p represents an integer of 0 to
 3. 2. The resist composition according to claim 1, wherein the polymeric compound (A1) further comprises a structural unit (a2) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains a lactone-containing cyclic group.
 3. The resist composition according to claim 1, wherein the polymeric compound (A1) further comprises a structural unit (a3) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains a polar group-containing aliphatic hydrocarbon group.
 4. A method of forming a resist pattern, comprising: using a resist composition according to any one of claims 1, 2, or 3 to form a resist film on a substrate; conducting exposure of the resist film; and developing the resist film to form a resist pattern.
 5. A polymeric compound comprising a structural unit (a0) represented by general formula (a1-0-14), (a1-0-15) or (a1-0-2) shown below and a structural unit (a5) represented by general formula (a5-1-1) shown below:

wherein R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R²² represents a group which forms an aliphatic monocyclic group with the carbon atom to which R²² is bonded; R²⁴ represents a group which forms an aliphatic polycyclic group with the carbon atom to which R²⁴ is bonded; each of R¹⁵ and R¹⁶ independently represents an alkyl group; Y² represents a divalent linking group; and X² represents an acid dissociable group; and

wherein in formula (a5-1-1) R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; X represents CH₂, CH₂CH₂, O, S or SO₂; each of R^(c) and R^(d) independently represents a hydrocarbon group which may have a substituent or a hydrogen atom, and R^(c) and R^(d) may be mutually bonded to form a ring; p represents an integer of 0 to
 3. 6. The polymeric compound according to claim 5, further comprising a structural unit (a2) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains a lactone-containing cyclic group.
 7. The polymeric compound according to claim 5, further comprising a structural unit (a3) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains a polar group-containing aliphatic hydrocarbon group.
 8. The resist composition according to claim 1, wherein the polymeric compound (A1) further comprises a structural unit (a0) represented by general formula (a0-0-1) shown below:

wherein R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R² represents a divalent linking group; and R³ represents a —SO₂— containing cyclic group.
 9. The polymeric compound according to claim 5, further comprising a structural unit (a0) represented by general formula (a0-0-1) shown below:

wherein R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R² represents a divalent linking group; and R³ represents a —SO₂— containing cyclic group. 